Addiction (1999) 94(9), 1397± 1412

RESEARCH REPORT

Family and friends’ in¯ uences on the uptakeof regular smoking from mid-adolescence toearly adulthood

PATRICK WEST, HELEN SWEETING & RUSSELL ECOB

MRC Social and Public Health Sciences Unit, Glasgow, Scotland, UK

Abstract

Aims. To examine the effect of family and friends’ smoking on uptake of regular smoking among young

people from mid-adolescence to early adulthood; whether such effects are time limited, vary by social class andgender, and the extent to which uptake precedes or follows friends’ smoking. Setting. The West of Scotland.

Design and participants. A longitudinal survey of 1009 15-year-olds interviewed at baseline, followed-up

at 16, 18, 21 and 23 years of age, using interviews and postal questionnaires. Measurements.

Self-reported measures of smoking were used, allowing analysis of the uptake of regular smoking (1 1 cigarette

per day) between 15 and 23, and in the periods 15± 16, 16± 18 and 18± 21 years. Measures of parental andsibling smoking and social class were obtained at baseline and respondents’ reports of friends’ smoking at 15

and 18 years. Findings. Regular smoking more than doubled between 15 (14%) and 23 (36%). Adjusted

for other factors, no independent effect of parental smoking on uptake in any period was observed, an effectof sibling smoking being con® ned to uptake between 15 and 16. Friends’ smoking at 15 increased the

likelihood of uptake up to 10 times over the next year, but did not extend to later years; that at 18 increased

it up to three times between 18 and 21. These effects did not vary by gender or social class. Further analysisrevealed a strong effect of friends’ smoking at age 18 on earlier as well as later uptake. Conclusions.

Contrasting with prevalent assumptions, the period from mid-adolescence to early adulthood is important for

uptake of regular smoking, and in particular reveals friends’ smoking to be of continuing signi® cance,especially around school-leaving when friendship networks often change markedly.

Introduction

Despite the decline in smoking among adults inBritain and elsewhere, children and young peo-ple continue to take up smoking in increasingnumbers. Successive studies of Britishschoolchildren have shown consistently that byage 11 around a third have already tried smok-ing, by age 15 a quarter or more are ª regularº(weekly) smokers, and that from the ® rst of thesestudies in 1982 (Dobbs & Marsh, 1983) to the

most recent in 1996 (Jarvis, 1997: Barton &Jarvis, 1997) regular smoking among 15-year-olds increased from around 25% to 30%. Muchless is known about the uptake of smoking in thepost-school period, though judging by rates ofcurrent smoking among young adults (43% ofmales, 36% of females at age 20± 24 in the 1996British General Household Survey (Thomas et

al., 1998) it is clear that a signi® cant minority ofall smokers start smoking after age 16. The

Correspondence to: Patrick West, MRC Social and Public Health Sciences Unit, 6 Lilybank Gardens, GlasgowG12 8RZ, Scotland, UK.

Submitted 15th October 1995; initial review completed 1st December 1998; ® nal version accepted 12th March1999.

ISSN 0965± 2140 print/ISSN 1360-0443 online/99/091397± 16 Ó Society for the Study of Addiction to Alcohol and Other Drugs

Carfax Publishing, Taylor & Francis Limited

1398 Patrick West et al.

common assumption that the uptake of smokingtypically occurs in early to mid-adolescence hasobscured the potential importance of processesoccurring in the post-school period, particularlyin respect of the key transition to regular smok-ing.

This assumption has also underpinned a vol-uminous research tradition, still predominantlycross-sectional in design, concerned to docu-ment the correlates and ª causesº of smoking inchildren and younger adolescents over thisperiod, a major emphasis of which has been onthe relative importance of smoking among familymembers and peers (e.g. Banks et al., 1978;Pederson & Lefcoe, 1985; Van Roosmalen &McDaniel, 1989). Following Flay et al. (1983), itis usually thought that family in¯ uences are mostimportant in the early stages of smoking, peerin¯ uences in initiation and experimentation, andinternal in¯ uences such as attitudes and inten-tions for habituation and maintenance (regularsmoking). Much of the research on this issuehas, however, been contradictory, in large partbecause investigators continue to make compari-sons between smokers and non-smokers at anystage in a smoking career, thus con¯ ating effectsparticular to different stages in the process ofbecoming a smoker (Flay et al., 1983). Evenamong the later generation longitudinal studies(e.g. Chassin et al., 1984; Semmer et al., 1987;McNeil et al., 1988), which have the potential toidentify antecedents to change in smoking behav-iour, investigators have tended to con¯ atein¯ uences on uptake with those on maintenanceover time (Conrad et al., 1992), a problem whichmakes it dif® cult to sort out the temporalsequence of events, most notably in relation tothe crucial question of whether smokers selectfriends who smoke or whether having smokingfriends precedes onset or change (West &Michell, 1998). A further problem arises fromthe model of the smoking process itself, since theassumption that it is largely a feature of early tomid-adolescence means it is not clear whetherthe stages and related in¯ uences operating atthese ages extend to later onset smoking andparticular transitions such as the uptake of reg-ular smoking in the post-school period. Becauseage and stage are con¯ ated, it may be thoughtthat internal in¯ uences replace those of familyand friends in older adolescence.

Given the focus on children and younger ado-lescents, and a related research design which is

typically school-based with limited follow-up,there is very little information about the extent towhich the effects of family or friends’ smokingpersist over time into late adolescence and earlyadulthood. To our knowledge there are only sixrelevant studies, all of which suggest that theseeffects may be in¯ uential in later onset smoking.Thus, Pulkinnen (1983), in an 8-year follow-upof Finnish adolescents, reported signi® cant cor-relations between parental and peer smoking atage 14 and a measure of smoking at age 20.Similar results were found in a follow-up of11-year-olds in the MRC/Derbyshire study(Swan, Murray & Jarrett, 1991), a small effect ofparental smoking, and reported ª peer pressureº ,being observed on regular smoking at age 21± 22.Newcomb, McCarthy & Bentler, (1989) alsofound a signi® cant effect of earlier peer smokingon smoking in young adulthood among US 7±9th-graders followed up 8 years later, althoughthis was limited to ª smoking within the past 4yearsº and did not extend to (current) smokingquantity. Pederson & Lefcoe (1986), followingUS 10-year-olds, found that increased smokingwas more common if parents and peers smoked,and that it was also related to an increase in peersmoking between ages 10 and 18. More recently,é ygard et al. (1995), in a 10-year follow-up ofNorwegian 11± 14-year-olds, similarly found thatfriends’ smoking in adolescence predicted ª dailysmokingº in early adulthood, although (exclud-ing baseline smokers) no independent effect wasfound on uptake over this period, the onlysigni® cant predictor being mother’ s smoking.Finally, Chassin et al. (1991), following-up US6± 12th-graders, found that those who becameregular smokers by early adulthood weresigni® cantly more likely to have had parents andfriends who smoked in adolescence than thosewho remained non-smokers, the effect of thelatter being particularly strong. Although theeffect for ª late onsetº was less pronounced thanthat for ª early onsetº smokers, the authors spec-ulated that the effect of friends’ smoking mighthave been greater if more proximal measures hadbeen available.

Many of the problems already identi® edextend to these studies of later adolescence. Eachof the ® rst three studies above fails to distinguisheffects on the maintenance of smoking fromeffects on uptake within the follow-up period.As é ygard et al.’ s (1995) study reveals, quitedifferent results may be obtained from analyses

Family and friends’ in¯ uences on regular smoking 1399

which include and exclude baseline smokers.Only the studies of Pederson & Lefcoe (1986)and Chassin et al. (1991) focus speci® cally onchange, and only the latter on a particular smok-ing transition, the uptake of regular smoking.Furthermore, to maximize the advantages of alongitudinal analysis, it is important to dis-tinguish between short- and long-term effects offamily and peer smoking since an effect may berestricted to one part of a follow-up period andª wear offº , or even reverse, over time. In respectof peer in¯ uences, this could be of majorsigni® cance since changing friendship networksduring adolescence mean an effect of peersmoking could, as suggested by Chassin et al.

(1991), be underestimated by the lack of proxi-mal measures.

This paper is concerned with the relativeimportance of family and friends’ in¯ uences onthe uptake of smoking over this under-researched period of mid-adolescence to earlyadulthood, and speci® cally focuses on the keytransition from non- or experimental smoker toregular smoker. It is based on a longitudinalstudy of young people in the West of Scotlandwho are being followed-up over the youthÐ adulttransition and has ® ve main aims: ® rst, todescribe the prevalence of regular smoking overan 8-year period from age 15 to 16, 18 and 21 toage 23; secondly, to examine the bivariate associ-ations with, and independent effects of, parental,sibs’ and friends’ smoking on the uptake of reg-ular smoking by young people over this period oftime; thirdly, to ascertain the extent to which theeffect of friends’ smoking on uptake is age-limited or more enduring over time; fourthly, toexamine the extent to which such effects varybetween young people, speci® cally those of dif-ferent gender and social class; and ® fthly, toexamine how changes in friendship groupsbetween age 15 and 18 are related to the uptakeof regular smoking both within this age periodand after age 18.

Methods

Background, sample and design

The data are derived from the youngest cohort ofthe West of Scotland Twenty-07 Study: Healthin the Community (Macintyre et al., 1989), alongitudinal study of three cohorts aged 15, 35and 55 at the time of the baseline survey in1987/88. To date, they have been followed-up

on four occasions; ® rst via postal questionnaireat the age of 16 (1988), secondly via interviewaged 18 (1990), thirdly again via postal question-naire aged 21 (1993), and most recently viainterview aged 23/4 (1995/6). The data referredto here come from baseline interviews withrespondents (and their parents) together with allsubsequent sweeps.

The study is located in the Central ClydesideConurbation (CCC), a predominantly urbanarea centred around Glasgow city. Each cohortwas sampled in the same way using StrathclydeRegion’ s Voluntary Population Survey (VPS), anenhanced electoral register (Black, 1985) whichpermits the identi® cation of individuals ofspeci® ed age and sex within households. Thesample was selected from the VPS using a two-stage strati® ed random procedure based on post-code sectors and targeted individuals withinsectors selected with a probability proportionalto the total population (Ecob, 1987). Theresponse rate at baseline was 65% (excludingmovers prior to ® rst contact) yielding anachieved sample of 1009 respondents, in whom995 parental interviews were also completed.The sample is representative of the sex ratio ofthe population of 15-year-olds in the CCC andof socio-economic indicators of their householdsobtained from the 1991 British Census (Der,1998). Of the baseline participants, 854 (85%)completed a postal questionnaire 1 year later,908 (90%) were interviewed at age 18, 806(80%) completed a second postal questionnaireaged 21, and 676 (67%) were reinterviewed inthe last sweep aged 23/4. In general, bias due toattrition has been relatively slight although, asTable 1 shows, at each follow-up losses havebeen greater among males (statisticallysigni® cant only at postal contacts), those frommanual social class backgrounds and (baseline)regular smokers. The result of this is that theprevalence of regular smoking in the cohort isprobably underestimated.

Twenty-07 respondents are interviewed typi-cally at home. This is not the preferred methodof conducting research on children’s or youngpeople’ s smoking (and other proscribed and/orsensitive topics) (McKennell, 1980), most stud-ies using self-complete questionnaires in theschool setting with either a real (e.g. Jarvis,1997) or bogus (e.g. Chassin et al., 1991)method of measuring cotinine levels. In cogni-zance of this, considerable efforts have been

1400 Patrick West et al.

Table 1. Baseline characteristics (aged 15) of Twenty-07 participants (part) and non-participants (non-part) at follow-upsaged 16, 18, 21 and 23: percentages and (numbers)

Sex Social class Smoking

Males Females Non-Man Man Regular Other

Baseline 47.8 52.2 41.3 58.7 14.0 86.0(482) (527) (410) (582) (141) (863)

16 part 46.1 53.9* 42.9 57.1* 12.1 87.9***(394) (460) (361) (481) (103) (747)

non-part 56.8 43.2 32.7 67.3 24.7 75.3(88) (67) (49) (101) (38) (116)

18 part 47.4 52.6 43.1 56.9*** 13.2 86.8*(430) (478) (386) (510) (119) (785)

non-part 51.5 48.5 25.0 75.0 22.0 78.0(52) (49) (24) (72) (22) (78)

21 part 46.2 53.8* 44.8 55.2*** 12.6 87.4**(372) (434) (356) (438) (101) (701)

non-part 54.2 45.8 27.3 72.7 19.8 80.2(110) (93) (54) (144) (40) (162)

23 part 47.0 53.0 44.2 55.8** 12.3 87.7*(318) (358) (295) (373) (83) (591)

non-part 49.2 50.8 35.5 64.5 17.6 82.4(164) (169) (115) (209) (58) (272)

* p , 0.05, **p , 0.01, ***p , 0.01.

made throughout to generate conditions underwhich respondents would answer truthfully. Thiswas particularly important at baseline when, tomaximize privacy and con® dentiality, interview-ers operated in pairs, one interviewing parent(s)while the other interviewed the 15-year-old,almost always in another room in the house. Theextent to which the ª methodº was successful isindicated by an analysis of responses to a ques-tion asked 3 years later relating to the agerespondents started smoking. Of those whoreported starting before 16 (and who thereforeshould have admitted it at the baseline interview)only 13/262 (5%) failed to do so. Under tightlycontrolled conditions, therefore, the home inter-view method does not appear to result in anyserious under-reporting of smoking among 15-year-olds, although this could have occurred atboth time points. There is no reason to suppose,however, that either of the postal contacts(addressed directly to the respondent with aprepaid return envelope) or the subsequenthome interviews at 18 and 23 resulted in con-cealment of smoking.

MeasuresThe measures refer to respondents’ own smokingbehaviour at each of the ® ve data points, family

in¯ uences represented by the smoking behaviourof parents and siblings (at age 15) and friends’smoking as reported by respondents at 15 and18.

Respondents’ smoking

Over the course of successive follow-ups, ques-tions about smoking behaviour changed from aformat based on the British national studies ofschoolchildren (Jarvis, 1997) to one more closelyre¯ ecting their adult status. At baseline, and inthe ® rst postal follow-up at age 16, identicalwording was used to ask respondents whetherthey had never smoked, tried smoking once ortwice, used to smoke, or whether they currentlysmoked occasionally (sometimes) or regularly,and if so how many cigarettes (including roll-ups) they smoked per week. At 18, respondentswere asked whether they currently smoked (evenjust occasionally), and if so how many cigarettesthey smoked per day or week, or if not whetherthey had ever smoked, a subsidiary questionestablishing whether they had tried smokingonce or twice. At age 21 and 23, respondentswere asked the same questions about currentsmoking and whether they had ever smoked inthe past, but those answering ª noº were not

Family and friends’ in¯ uences on regular smoking 1401

asked the subsidiary relating to whether or notthey had ever tried smoking.

This change in format means that while reg-ular smokers can be identi® ed at every timepoint, it is not possible to identify experimentalsmokers consistently since after age 18 ª triersºwere not ascertained. For this reason, togetherwith small numbers of ex-smokers, the analysisfocuses on the key transition at this age, theuptake of regular smoking between age 15 and23. Regular smokers are de® ned as those smok-ing at least one cigarette per day, a de® nitiondiffering from that used in most studies of child-hood where the criterion is typically 1 1cigarette per week, but consistent with otherstudies of older adolescents (Pederson & Lefcoe,1985) and with earlier analyses reported on thiscohort (Green et al., 1991). The other relevantcategories are: experimental smokers (de® ned asª triersº plus those ª occasionalº smokers smok-ing less than one cigarette per day), ex-smokerswho from 16 onwards consist principally of thosede® ning themselves as experimental smokers atprevious sweeps; and never smokers who includean increasing proportion of respondents de® ningthemselves previously as experimental or ex-smokers, but never regular smokers.

Parental smokingUnlike almost all studies of smoking in child-hood and adolescence, at age 15 informationabout parental smoking was obtained from par-ents as well as respondents. A comparisonbetween the two reports of current parentalsmoking (regular or occasional) reveals the levelof agreement to be very high for both mothers(kappa 5 0.96) and fathers (kappa 5 0.88). Noneof the analyses reported here, which refer toregular smoking (1 1 cigarette per day) in any(one or both) parent, is altered more than mar-ginally if respondents’ reports of parental smok-ing are used instead of parents. On the parents’own de® nition, 44% of mothers and 51% offathers living in the household were regularsmokers, one or both of them smoking in 63% ofcases.

Siblings’ smokingInformation on siblings’ smoking is availableonly from respondents, and only at baseline, and

distinguishes older and younger brother(s) and/or sister(s) in terms of being current (regular oroccasional), past or never smokers. Where morethan one older or younger sibling smoked,respondents were instructed to report on thenearest in age. In the analysis reported here, it isrestricted to one simple variable distinguishingbetween any (current) sibling smoking (26%)and none (including those with no sibs).

Friends’ smokingFriends’ smoking was ascertained at baseline inthe context of a number of questions about thecharacteristics of friendship groups using a stan-dard response set. Respondents were asked tosay how many of their friends smoked, theoptions being none, one, a few, half, most, allbut one and all, which for analytical purposes arecollapsed into three categories; none, ª someº(one plus a few) and ª mostº (half to all) (split-ting 30%, 55% and 16%). At age 18, respon-dents were asked an identical question aboutfriends’ smoking characteristics (comparable cat-egories splitting 20%, 53% and 26%). Thismethod of obtaining data about friends’ smokinghas been used widely in research on children’sand young people’ s smoking but is open to thecriticism that smokers overestimate (and non-smokers underestimate) the proportion (or num-ber) of friends who smoke (Urberg, Shyu &Liang, 1990). While this may lead to some exag-geration of the effect of friends’ (non) smokingon the smoking behaviour of respondents, in thefew studies with data on friends’ actual smoking(Hunter et al., 1987; Eiser et al., 1991) the® ndings are similar to those based on perceivedestimates.

In addition to those variables, in order toexamine the extent to which the effects of familyand friends’ smoking might vary for differentyoung people, respondents’ gender and socialclass are taken into account. Social class is mea-sured by the occupation of the head of house-hold (HoH), as derived from informationprovided by parents at interview when respon-dents were aged 15, and de® ned by the father’scurrent or previous occupation if not currentlyemployed or, in the absence of a father ® gure, amother’ s current or previous occupation. Here, asimple two-fold classi® cation is used, distin-guishing respondents from non-manual (41%)

1402 Patrick West et al.

Table 2. Numbers taking up regular smoking (1 1 cig/day) aged 15± 16, 16± 18, 18± 21, 21± 23and 15± 23 among previous never or experimental smokers

Age Never/Exp Regular Ex Lost

15 756 141 107 N/A

16 566 65 20 105

18 461 44 29 32

21 332 39 51 39

23 259 4 6 63

15± 23 342 130 44 240

and manual backgrounds. None of the analysesreported are altered more than marginally with afuller social class classi® cation.

Analyses

To examine the question of whether the effectsof family and friends’ smoking persist through-out the period 15± 23 years or are restricted toparticular ages within that period, the mainanalysis reported in this paper refers to theuptake of regular smoking between ages 15± 16,16± 18 and 18± 21 (but not 21± 23 where numbersare too small). This focus on uptake means thatregular smokers and ex-smokers at baseline areexcluded from all analyses, the comparisongroup for each speci® c analysis comprising onlythose who reported themselves either neversmokers or experimental smokers at the begin-ning of each period, i.e. at 15, 16 and 18. In thecase of the whole period, age 15± 23, the com-parison group consists of those who were neveror experimental smokers at age 15 only.

The numbers on which the analyses are basedare presented in simpli® ed form in Table 2,® gures for sample losses at each sweep, but notbetween sweeps, being shown. In the case ofuptake in each of the three speci® c periods, thenumbers in each category (including ex-smokers

and losses) sum to the total of non- and exper-imental smokers at the beginning of each period.Thus, among 756 never or experimental smokersat baseline, 566 remained in that category at age16, 65 became regular smokers, 20 describedthemselves as ex-smokers and 105 were lost tothe sample at that stage, the comparison(shaded) being between the ® rst two categories.Numbers for analyses of uptake between 16 and18, and 18 to 21, are similarly derived. In thecase of the 15± 23 comparison, however, whilethe ® gures also sum to 756, they are not cumu-lative within categories since they neither takeaccount of regular smokers lost to the sample byage 23 nor of the changing de® nition of ex-smokers over time.

We examine ® rst bivariate associationsbetween the uptake of regular smoking and fam-ily and friends’ smoking together with genderand social class, using the chi-square statistic toestablish statistical signi® cance. Next, usinglogistic regression, we examine the independenteffects of each of the variables on the outcomes,summarizing the effects as a series of odds ratios.Finally we present a bivariate, and multivariate,analysis of changes in the smoking characteristicsof friendship groups between age 15 and 18 andthe uptake of regular smoking within and afterthat period.

%

015

Age16 18 21 23

10

20

30

40

13.5 14.5

20.7

24.7

30.8 30.8

39.1

34.2

41.5

31.5

Family and friends’ in¯ uences on regular smoking 1403

Figure 1. Prevalence of regular smoking (1 1 cig./day) bySex at ages 15, 16, 18, 21 and 23 years ( h male, 7 female).

rates among the former and higher quit ratesamong the latter after age 18.

Predictors of regular smokingTable 3 presents the bivariate associations witheach of the independent variables for uptakebetween ages 15± 16, 16± 18 and 18± 21, with thecumulative results for the whole 8-year follow-upperiod (age 15± 23) shown in the ® nal column,thus replicating the time interval of most othercomparable studies.

Considering ® rst the ® ndings for the wholefollow-up period, it can be seen that amongbaseline non- or experimental smokers thosewith parents who smoked were no more likely tobecome regular smokers than those whose par-ents did not, nor was there any association withsibling smoking. The uptake of regular smokingbetween age 15 and 23 was, however, associatedsigni® cantly with friends’ smoking behaviour atage 15, 44% of those with ª mostº friends smok-ing becoming regular smokers over this periodcompared with 18% with no smoking friends.No difference was observed between respon-dents from different social class backgrounds,but males (33%) were signi® cantly more likely totake up regular smoking than females (23%).

This picture, however, conceals considerablevariation in the pattern of association with up-take at different ages, and reveals the 15± 16 ageperiod as being quite distinct. Here, those re-spondents with parents who smoked weresigni® cantly more likely to become regular smok-ers within the next year (12%) than those with-out (7%). Similarly, those with a brother or sisterwho smoked were also more likely to take upregular smoking (18%) compared to those witheither no sibs or none who smoked (8%). Fur-thermore, a particularly strong association is ob-served between uptake in this period and friends’smoking at age 15, 28% of those with ª mostºfriends smoking becoming regular smokers be-tween age 15 and 16 compared to just 3% ofthose with no smoking friends. Finally, while inthis period there was no difference in uptakebetween the sexes, respondents from manualclass backgrounds were more likely to becomeregular smokers than those from non-manualbackgrounds. None of these variables (exceptrespondents’ sex at age 18± 21) is associatedsigni® cantly with the uptake of regular smokingeither between ages 16 and 18, or between 18 to

Findings

Prevalence of regular smoking

Figure 1 shows the prevalence of regular (1 1cigarette per day) smoking for males and femalesat each age from 15 through 23. On thisde® nition, at baseline 14% of the sample wereregular smokers, a further 40% [36% had triedsmoking once or twice, 4% smoked occasionally( , 1 cigarette per day)] were experimenters,11% claimed to have given up smoking and 36%to have never smoked. One year later at age 16,regular smoking had increased to 23%, at 18 to31%, and at ages 21 and 23 to 36%. In sum-mary, rates of regular smoking doubled betweenage 15 and 18, highlighting the importance ofin¯ uences in the immediate post-school period,and by early adulthood had risen two-and-a-halftimes to involve over a third of all respondents.In this sample, no signi® cant differences betweenthe sexes in any category of smoking are ob-served until age 23 when males (42%) reportedhigher rates of regular smoking than females(32%), a consequence both of higher uptake

1404 Patrick West et al.

Table 3. Percentage (and numbers) taking up regular (1 1 cig/day) smoking aged 15± 16, 16± 18, 15± 21 and 15± 23 byparental, sibs’ and friends’ smoking (aged 15), sex and social class (HOH)Ð bivariate associations

15± 16 16± 18 18± 21 15± 23

yes no yes no yes no yes no

Parentalnone/neither 7.2 92.8* 9.2 90.8 11.6 88.4 24.3 75.7

(18) (233) (19) (187) (17) (129) (45) (140)one or both 12.3 87.7 8.2 91.8 8.5 91.5 27.7 72.3

(44) (314) (23) (258) (18) (194) (74) (193)

Sibsnone/no sibs 8.1 91.9*** 8.8 91.2 10.3 89.7 26.2 73.8

(40) (452) (36) (373) (31) (270) (100) (281)one or more 17.9 82.1 8.4 91.6 11.6 88.4 33.0 67.0

(24) (110) (8) (87) (8) (61) (29) (59)

Friendsnone 2.8 97.2*** 7.2 92.8 8.4 91.6 17.6 82.4***

(7) (242) (16) (206) (14) (152) (35) (164)some 10.6 89.4 9.2 90.8 12.7 87.3 31.7 68.3

(30) (253) (21) (208) (22) (151) (66) (142)most 27.8 72.2 13.0 87.0 9.4 90.6 43.8 56.3

(27) (70) (7) (47) (3) (29) (28) (36)

Sexmale 9.2 90.8 9.4 90.6 14.1 85.9* 32.5 67.5*

(28) (276) (23) (222) (25) (152) (74) (154)female 11.3 88.7 8.1 91.9 7.2 92.8 23.0 77.0

(37) (290) (21) (239) (14) (180) (56) (188)

Social classnon-man 7.4 92.6* 9.3 90.7 10.6 89.4 27.4 72.6

(21) (262) (22) (214) (19) (160) (60) (159)man 12.9 87.1 8.4 91.6 10.7 89.3 27.8 72.2

(44) (298) (22) (241) (20) (167) (69) (179)

Total 10.3 89.7 8.7 91.3 10.5 89.5 27.5 72.5(65) (566) (44) (461) (39) (332) (130) (342)

* p , 0.05, **p , 0.01, ***p , 0.001.

21. In short, these ® ndings are quite differentfrom those observed over the longer period, andmoreover quite unique to the 15± 16 period sincenone of the independent variables is signi® cantlyrelated to uptake at later ages. The picture is onein which the effects of family members’ smoking,and friends’ smoking, appears to ª wear offº overtime, the former being rendered invisible, thelatter being reduced in strength.

Table 4 shows the results of the logistic regres-sions which estimate the size of the independenteffects of each of the variables on the likelihoodof becoming a regular smoker in each period asa series of adjusted odds ratios (OR with 95%con® dence intervals). The results for the period15± 23 are presented for comparative purposes.In addition, in order to test the extent to whichfriends’ smoking is a proximal in¯ uence, esti-mates of the effect of friends’ smoking at age 18

on the likelihood of taking up regular smokingover the next 3 years are calculated. Each of themodels shown is a good ® t to the data, only one(of 50) ® rst or second order interaction termswith respect to gender or social class being statis-tically signi® cant. As this is likely to haveoccurred by chance, the main effect models areconsidered reliable.

The ® ndings show that once other variablesare taken into account, the effect of parentalsmoking on uptake between age 15 and 16 isrendered non-signi® cant, other analyses (notshown) revealing the bivariate association in thisperiod to be explained by sibling smoking. Theeffect of the latter remains signi® cant, the oddsof becoming a regular smoker in this periodbeing doubled (OR 1.99, p , 0.05) by a brotheror sister who smoked. By comparison, the effectsof friends’ smoking are much larger. Among

Family and friends’ in¯ uences on regular smoking 1405

Table 4. Relative odds of taking up regular (1 1 cig/day) smoking aged 15± 16, 16± 18, 18± 21 and 15± 23 and 15± 23 byparental smoking, sibs’ smoking and friends’ smoking (aged 15), sex and social class, and 18± 21 by friends, smoking at age

18 (odds adjusted simultaneously for other factors)

15± 16 16± 18 18± 21 15± 23 18± 21

Parental smokingnone/neither 1.00 1.00 1.00 1.00 1.00one or both 1.32 0.86 0.73 1.14 0.68

(0.71, 2.43) (0.45, 1.66) (0.36, 1.51) (0.72, 1.80) (0.33, 1.41)

Sibs smokingnone/no sibs 1.00 1.00 1.00 1.00 1.00one or more 1.99* 1.03 0.96 1.29 0.93

(1.10, 3.61) (0.45, 2.32) (0.37, 2.47) (0.74, 2.24) (0.36, 2.41)

Friends smoking (aged 15) (aged 15) (aged 15) (aged 15) (aged 18)none 1.00 1.00 1.00 1.00 1.00some 3.74** 1.34 1.79 2.30** 1.52

(1.60, 8.74) (0.67, 2.67) (0.84, 3.79) (1.41, 3.74) (0.63, 3.70)10.74*** 1.44 0.84 2.94** 3.29*

(4.38, 26.36) (0.50, 4.16) (0.18, 3.99) (1.50, 5.69) (1.19, 9.14)

Sexmale 1.00 1.00 1.00 1.00 1.00female 1.24 0.83 0.46 0.55* 0.52

(0.71, 2.18) (0.42, 1.57) (0.22, 1.04) (0.36, 0.86) (0.25, 1.09)

Social classnon-manual 1.00 1.00 1.00 1.00 1.00manual 1.58 1.01 0.78 0.93 0.75

(0.87, 2.86) (0.53, 1.93) (0.38, 1.60) (0.60, 1.45) (0.36, 1.55)Goodness of ® t ( c 2) 45.78 39.36 40.81 48.40 42.51

(p 5 0.181) (p 5 0.322) (p 5 0.196) (p 5 0.081) (p 5 0.211)Sample size 603 485 356 448 355

* p , 0.05, **p , 0.01, ***p , 0.001.

respondents with ª someº friends who smoked atage 15 the likelihood of becoming a regularsmoker 1 year later was almost four times (OR3.74, p , 0.01) as large as those with no smokingfriends, and among those with ª mostº friendssmoking 10 times as large (OR 10.74,p , 0.001). Furthermore, while no signi® cant ef-fect of friends’ smoking at 15 is observed onuptake in either of the later periods, a differentresult is obtained when friends’ smoking at age18 is used in an analysis of uptake between 18and 21. In this case, respondents with ª mostºfriends smoking were three times (OR 3.29,p , 0.05) as likely to become regular smokersover this period compared with those who at age18 had no friends who smoked. The analysesshow no independent effect of social class, thebivariate association with uptake in the 15± 16-year period being accounted for by friends’rather than family smoking. Finally, indepen-dently of all other variables, females were onlyhalf as likely to become regular smokers as malesin the period 18± 21.

The results of these analyses, therefore, dem-onstrate that the effect of friends’ smoking, andto a lesser extent that of siblings’ , is not consist-ent over time but operates only over a relativelyshort period to in¯ uence the uptake of smoking.Despite the substantial effect of friends’ smokingover the whole follow-up period, elevating theodds of regular smoking by a factor of three (OR2.94, p , 0.01), this is nevertheless a consider-able underestimate of its impact at an earlier,more proximal, time. Furthermore, as indicatedby the absence of interactions with both socialclass and gender, these effects appear to operateequally for males and females and respondentsfrom different backgrounds.

Change in friendship groups and the uptake of reg-ular smoking

The ® nding that the effect of friends’ smoking isof limited duration suggests that the processesinvolved are dynamic and relate closely tochanges in friendship networks. Although infor-

1406 Patrick West et al.

Ta

ble

5.

Per

centa

ge(a

nd

num

bers

)ta

kin

gup

regu

lar

smok

ing

(11

cig/

day)

age

d15±16,

16±18

and

18±2

1acc

ordi

ng

tofr

iends’

smok

ing

at

15

and

18

Pro

port

ion

of

frie

nd

ssm

oki

ng

atag

eU

pta

keof

regu

lar

15

smoki

ng

non

eso

me

most

18

non

eso

me

most

non

eso

me

most

non

eso

me

most

15

±16

yes

1.2

1.7

10

.5**

5.1

5.9

25.0

***

0.0

20.6

36

.4(1

)(2

)(4

)(3

)(8

)(1

8)

(0)

(7)

(16)

no

98.8

98.3

89

.594

.994.1

75.0

100.0

79.4

63

.6(8

2)

(117)

(34

)(5

6)

(128

)(5

4)

(8)

(27)

(28)

16

±18

yes

1.3

6.4

25

.8**

*0

.07.4

23.1

***

0.0

0.0

29

.2**

*(1

)(7

)(8

)(0

)(9

)(1

2)

(0)

(0)

(7)

no

98.8

93.6

74

.2100

.092.6

76.9

100.0

100.0

70

.8(7

9)

(102)

(23

)(5

5)

(113

)(4

0)

(6)

(24)

(17)

18

±21

yes

1.4

13.6

13

.3*

15

.77.7

22.6

20.0

5.6

11

.1(1

)(1

1)

(2)

(8)

(7)

(7)

(1)

(1)

(1)

no

98.6

86.4

86

.784

.392.3

77.4

80.0

94.4

88

.9(6

8)

(70)

(15

)(4

3)

(84)

(24)

(4)

(17)

(18)

*p

,0.0

5,

**p

,0

.01,

***p

,0

.001.

Family and friends’ in¯ uences on regular smoking 1407

Table 6. Relative odds of taking up regular (1 1 cig/day) smoking aged 15± 16, 16± 18 and 18± 21 by parental smoking,sibs’ smoking, friends’ smoking at 15 and 18, sex and social class (odds adjusted simultaneously for other factors)

15± 16 16± 18 18± 21

Parental smokingnone/neither 1.00 1.00 1.00one or both 1.20 0.71 0.68

(0.63, 2.28) (0.36, 1.43) (0.33, 1.42)

Sibs smokingnone/sibs 1.00 1.00 1.00one or more 1.79 0.84 0.92

(0.93, 3.43) (0.36, 1.97) (0.35, 2.38)

Friends (15)none 1.00 1.00 1.00some 3.00* 0.97 1.56

(1.25, 7.15) (0.46, 2.01) (0.72, 3.37)most 6.25** 0.66 0.65

(2.41, 16.20) (0.21, 2.03) (0.14, 3.17)

Friends (18)none 1.00 1.00 1.00some 1.64 10.04* 1.53

(0.53, 5.10) (1.31, 76.71) (0.63, 3.74)most 6.99** 50.91** 3.20*

(2.33, 20.91) (6.59, 390.33) (1.13, 9.06)

Sexmale 1.00 1.00 1.00female 1.27 1.08 0.49

(0.69, 2.32) (0.55, 2.14) (0.23, 1.03)

Social classnon-manual 1.00 1.00 1.00manual 1.52 0.85 0.72

(0.81, 2.85) (0.43, 1.69) (0.35, 1.51)

Goodness of ® t ( c 2) 81.34 61.51 77.16(p 5 0.951) (p 5 0.998) (p 5 0.608)

Sample size 569 483 355

* p , 0.05, **p , 0.01.

mation on this issue in the Twenty-07 study islimited, some evidence is available from dataabout friends’ smoking at age 15 and 18. Incombination, they allow us to categorize respon-dents in terms of the extent to which the smok-ing characteristics of friends (divided intoª noneº , ª someº and ª mostº ) remain stable orchange over that 3 year period, and the relation-ship of those friendship trajectories to the uptakeof regular smoking. The extent of change isconsiderable, less than half (47%) remaining inthe same smoking friendship category, 10% ofthose with no smoking friends at age 15 subse-quently being in groups with ª mostº friendssmoking, and 15% of those with ª mostº friendssmoking at 15 subsequently having no smokersamong their friends. Table 5 presents uptakerates according to friends’ smoking at both ages

over the periods 15± 16, 16± 18 and 18± 21, thusenabling some evaluation of the extent to whichuptake both precedes and ensues from changesin friendships.

Considering ® rst respondents who at age 15reported no friends smoking, it can be seen thatamong those who remained in non-smokinggroups at age 18 almost none took up smokingeither during that period or in the 3 years after-wards. Among those whose friends at age 18included ª someº smokers, uptake rates arehigher in the 3-year period both before and afterthat age. Among those exhibiting the greatestchange from friendship groups with no smokersat age 15 to those with ª mostº smokers at 18,the uptake rates are highest of all, a patternhowever which is most pronounced (and statisti-cally signi® cant) in the period prior to rather than

1408 Patrick West et al.

after age 18, notably between 16 to 18 when26% became regular smokers. A very similaroverall pattern is apparent among respondentswith ª someº smoking friends at age 15, thosewith ª mostº friends smoking three years laterhaving higher uptake rates in both periods beforethat age, 25% becoming regular smokersbetween age 15 and 16. With respect to respon-dents who at age 15 reported ª mostº friendssmoking, the focus of interest is those who byage 18 counted no smokers among their friends.None of them had become regular smokers inthe previous 3 years, while those who remainedin smoking friendship groups had the highestuptake rates of all.

These ® ndings not only testify to the consider-able variation in uptake rates according tochanges in the smoking characteristics of friend-ship groups over a relatively short time period,but also show that uptake appears to precedesuch changes rather than simply being conse-quential on them. This presents a contrast to theprevious analyses which show friends’ smokingto be antecedent to uptake, and as such suggestsa role for friendship selection.

To examine this further, and to assessspeci® cally the relative importance of friends’smoking at 15 and 18 on uptake both within andafter that period, another series of logistic regres-sions was conducted, the results of which arepresented in Table 6. These show that whenparental and sibling smoking, gender and socialclass, together with the two measures of friends’smoking are all considered together, the modelsare an extremely good ® t to the data for each ofthe three periods although, re¯ ecting small cellnumbers, the con® dence intervals of the esti-mates are wide. In these models, neither thesibling effect on uptake between age 15 and 16,nor the gender effect on uptake between 18 and21, remain signi® cant. The effect of friends’smoking at 15 on the uptake of regular smokingover the following year, though slightly reduced,remains signi® cant (OR 6.25, p , 0.01 forª mostº friends smoke), and as before is limitedto this period, while the effect of ª mostº friends’smoking at age 18 on uptake over the next 3years is actually slightly increased (OR 3.20,p , 0.05). In addition, and complementing thebivariate ® ndings, there is also an effect offriends’ smoking at age 18 on the uptake ofregular smoking in the previous 3 years. This isapparent both with respect to the earlier period,

when the odds of uptake between 15 and 16 areincreased seven times (OR 6.99, p , 0.01)among those with ª mostº friends’ smoking at 18,and even more so in the two following years,when the comparable odds are dramaticallyincreased (OR 50.91, p , 0.01).

Discussion

In this paper, we have examined the effects offamily and friends’ smoking on the uptake ofregular smoking between the ages of 15 and 23.This is a period which has received remarkablylittle attention in the literature largely because ofthe assumption that the uptake of smoking is afeature of early adolescence. In some measure, ofcourse, this is true. The ® ndings of the Twenty-07 study, in common with others, show thataround two-thirds (64%) of 15-year-olds alreadyhad some smoking experience. However, notonly were there some young people (15%) who® rst smoked after that time, but more impor-tantly a much larger proportion made the tran-sition from non- or experimental smoker toregular smoker, rates of regular smoking (1 1cigarette per day) more than doubling from 14%to 31% between age 15 and 18, and continuingto increase to 36% at age 23. This appliesequally to males and females up to age 18, butthereafter the differential uptake between thesexes results in a signi® cantly higher rate ofregular smoking among males at age 23. This isconsistent with the national picture for sex differ-ences in early adulthood (Thomas et al., 1998)and represents a reverse of the pattern among11± 15-year-olds which receives so much atten-tion.

Despite the similar sex ® ndings, it is probablethat the overall prevalence rates of regular smok-ing are somewhat underestimated in this sampleboth at baseline and, because of differential attri-tion, at follow-up. At 15 (1987), using the moreconventional criterion of weekly smoking, 18%were regular smokers compared with 25%(1986) for Scotland as a whole (Goddard & Ikin,1987). At age 23 (1995/6), 36% were dailysmokers compared with 39% among 20± 24 yearolds in Britain (1996) (Thomas et al., 1998).Although this may affect precise estimates ofuptake after age 16, there is no reason to supposethat the processes differ, and on any estimate itmeans that a substantial minority of young peo-ple take up regular smoking in the post-school

Family and friends’ in¯ uences on regular smoking 1409

period. Along with others, notably Chassin et al.

(1991), we think these later onset smokers meritmuch closer attention than they have receivedhitherto.

Although not entirely consistent, mostresearch ® nds a relationship between children’ sand adolescent’ s smoking and that of familymembers, the association generally being smallerin studies with a longitudinal design and amongolder adolescents. In the present study, no effectof parental smoking on the uptake of regularsmoking between 15 and 23 was found, a smallbivariate relationship between 15 and 16 beingaccounted for by the associated smoking behav-iour of brothers and sisters. These ® ndings sug-gest strongly that the impact of family in¯ uenceson the uptake of regular smoking is restricted toparticular (younger) ages and that without takingthe age speci® city of the effect into account amisleading picture can be generated. For exam-ple, é ygard et al.’ s (1995) ® nding that maternalsmoking doubled the rate of regular smoking ina cohort of 11± 14-year-olds over a 10-yearperiod is not necessarily inconsistent with the® ndings of the Twenty-07 study, in which weobserve an effect of parental smoking at age15± 16 only. We suggest that the in¯ uence offamily members’ smoking on the uptake of reg-ular smoking after age 16 is relatively slight andcon® ned to an effect of older siblings at oraround school-leaving age.

The ® ndings in respect of friends’ smoking areperhaps the most interesting yet also the mostcomplex. The analysis of uptake over the period15± 23 years reveals that those whose friends atage 15 consisted mainly of smokers were muchmore likely to take up regular smoking thanthose with no smoking friends. Although theeffect appeared to diminish over time, by age 23this still represented a threefold difference. Thisis consistent with the ® ndings of the few otherrelevant studies, including that of Chassin et al.(1991), the only exception being that of é ygardet al. (1995). However, in common with thepattern found for sibling smoking but in muchmore dramatic fashion, when the analysis ofuptake is examined within speci® c time periodsthe effect of friends’ smoking is shown to belimited to the age period 15± 16 where a 10-folddifference is observed between those with mostfriends smoking compared with those with none.Furthermore, when a similar analysis is conduc-ted using friends’ smoking at age 18 (rather than

15) the uptake of regular smoking over the next3 years is increased three-fold, not quite such amarked effect as at age 15 but substantial never-theless. Taken together, these ® ndings reveal theeffect of friends’ smoking to be extremely proxi-mal in nature, thus con® rming Chassin et al.’ s(1991) speculation and suggesting that similarresults might have been obtained for other peri-ods had a measure of friends’ smoking beenavailable at every time point. Comparisons overa longer time period, such as that between age15 and 23 in the Twenty-07 study, are likelytherefore to seriously underestimate the effect offriends’ smoking.

The overall picture emerging from these® ndings is one in which the effect of friends’smoking on the uptake of regular smoking in thepost-school period far outweighs that of familymembers’ . It is tempting to conclude, becausethe (longitudinal) analysis reveals friends’ smok-ing to be antecedent to uptake, that this meansfriends ª causeº smoking, perhaps via processesof peer pressure, and that there is no role forselection. The proximal nature of the relation-ship between friends’ smoking and uptake, how-ever, suggests the processes involved aredynamic and may relate to changes in friendshipnetworks which particularly characterize theperiod of later adolescence and early adulthood.This possibility receives support from another setof ® ndings on the relationship between theuptake of regular smoking and changes in thesmoking characteristics of friendship groupsbetween age 15 and 18. These analyses showthat while low and high uptake rates are associ-ated with ª stableº non-smoking and smokingfriendship groups respectively over this period,15-year-olds moving from high to low smokinggroups were also much less likely to becomeregular smokers and conversely those movingfrom low to high smoking groups were muchmore likely to become regular smokers. Althoughwe cannot rule out the possibility that thesedifferences in uptake rates were actually pre-ceeded by changes in friendships, the fact thatthe effect of future friends’ smoking persistswhen the smoking characteristics of currentfriends is taken into account, together with thefact that this is observed as early as the 15± 16period, more than 2 years prior to the secondmeasure of friends’ smoking, suggests stronglythat in some part young people select theirfriends on the basis of their smoking characteris-

1410 Patrick West et al.

tics. This interpretation would accord with the® ndings of those studies using sociometric meth-ods to investigate the relationship betweenfriends’ smoking which have shown a signi® cantrole for selection (Ennett & Baumann, 1994). Itis equally compatible with the view that childrenand young people in some part choose thein¯ uences they experience (Hill, 1990; Eiser etal., 1991). An alternative, or complementary,explanation is that stable friendship groupschange their behaviour together.

The ® ndings also reveal that the effect offriends’ (and family members’ ) smoking onuptake is consistent for both males and femalesand young people from different social classbackgroundsÐ there are no signi® cant interac-tion effects. Although not shown in this paper, itis also the case that the effect of friends’ smokingdoes not vary signi® cantly by labour market pos-ition, being similar both among 16-year-oldsremaining in school compared to those who hadleft, and among 18-year-olds whether in work,unemployed or in tertiary education. Thus,despite the different social contexts, and differ-ent rates of uptake (markedly higher among theunemployed), the processes involved appear tobe similar. It is possible therefore that they relateto general transitions, and associated changes infriendship around ages 16 and 18, rather thanany speci® c labour market experience. The® nding that the effect of friends’ smoking isproximal rather than of longer duration isentirely consistent with the volume of friendshipchange implied by such transitions.

Such explanations, however, stress the wayfriends’ characteristics might impact on smokingand account less well for any selection effect.Another possibility is that smoking is selectivefor a range of social positions, statuses and expe-riences, including that of friendships. In a pre-vious paper (West & Sweeting, 1996), we haveshown that independently of class of backgroundearlier smoking is related strongly to later labourmarket position, those in tertiary education atage 18 being very unlikely to have been smokersat age 15, those who became unemployed havingmuch higher rates. Similar results have beenreported by Glendinning, Shucksmith &Hendry, (1994) in a study of young people inScotland, and by Chassin et al. (1992) in theUnited States. What these ® ndings suggest isthat (non) smoking is not only associated withparticular life-styles in adolescence but that such

life-styles re¯ ect future adult roles, perhaps by aprocess of anticipatory socialization. In a similarway the uptake of regular smoking might antici-pate the smoking characteristics of future friendseither through choice or simply because suchlabour market trajectories, and associated life-styles, make contact with smokers more likely.

Overall, the evidence points to the fact thatresearch into the effects of family and friends’smoking has been over-circumscribed by amodel of uptake assumed to occur betweenchildhood and adolescence. The assumption hasbeen that later-onset smokers smoke for differentreasons. The ® ndings from the Twenty-07 studyhighlight not only the importance of the lateradolescent and early adulthood periods for theuptake of regular smoking, but also indicate thatsimilar processes of peer selection and peerin¯ uence on smoking occur in the post-schoolperiod as occur earlier on. The settings, ofcourse, are different, but the need to understandthe processes more fully and generate appropri-ate health education strategies to different con-stituencies of potential smokers has never beenmore apparent.

Acknowledgements

The authors would like to thank Sally Macintyre,Lynn Michell and Manfusa Shams for commentson earlier drafts of this paper, and LouiseO’Neill and John Gilchrist for help in preparingtables and ® gures. They are supported by theMedical Research Council of Great Britain.

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