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The Effect of Lottery Scratch Tickets and Donation
Offers on Response Fraction: A Study and Meta-
Analysis
Article in Field Methods · February 2012
DOI: 10.1177/1525822X11424549
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2012 24: 112 originally published online 27 December 2011Field MethodsTerry Boyle, Jane Heyworth, Jenny Landrigan, Robin Mina and Lin Fritschi
Response Fraction: A Study and Meta-AnalysisThe Effect of Lottery Scratch Tickets and Donation Offers on
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The Effect ofLottery ScratchTickets andDonation Offers onResponse Fraction:A Study andMeta-Analysis
Terry Boyle1, Jane Heyworth2, Jenny Landrigan2,Robin Mina2, and Lin Fritschi1
AbstractMonetary incentives are the most effective way of increasing response topostal questionnaires; however, mailing currency is prohibited in manycountries. Hence, nonmonetary incentives, such as lottery scratch ticketsand donation offers, have been used. The effectiveness of different typesof nonmonetary incentives is unclear, however. Two randomized con-trolled studies and meta-analyses were conducted to investigate the effectof two types of nonmonetary incentives on response. In the first study, the
1 Western Australian Institute for Medical Research, The University of Western Australia,
Nedlands, Western Australia, Australia2 School of Population Health, Faculty of Medicine, Dentistry, and Health Sciences, The
University of Western Australia, Crawley, Western Australia, Australia
Corresponding Author:
Terry Boyle, Western Australian Institute for Medical Research, The University of Western
Australia, B Block, Hospital Avenue, Sir Charles Gairdner Hospital, Nedlands, Western
Australia 6009, Australia
Email: [email protected]
Field Methods24(1) 112-132
ª The Author(s) 2012Reprints and permission:
sagepub.com/journalsPermissions.navDOI: 10.1177/1525822X11424549
http://fm.sagepub.com
authors found that participants who received an unconditional lotteryscratch ticket at invitation were 24% more likely to take part, while in thesecond study, the authors found that unconditional lottery scratch ticketsand donation offers had a similar effect on response. The meta-analysesshow that unconditional lottery scratch tickets significantly increase thechance of response by 9%, conditional scratch tickets have no effect, anddonation offers cause a nonsignificant 4% increase in the chance ofresponse. Unconditional lottery scratch tickets provide a modest increasein the likelihood of response.
Keywordsepidemiologic methods, questionnaires, response rate, incentives
Unconditional monetary incentives have been found to be the most effective
way of increasing response fractions to postal questionnaires (Edwards et al.
2005; Edwards et al. 2009). Sending currency in the regular mail is prohibited
in Australia (Australia Post 2009) and many other countries (Royal Mail Group
2010); however, nonmonetary incentives, such as lottery scratch tickets and
donation offers, have been used. A recent meta-analysis found that nonmone-
tary incentives increase the odds of response by 15% (95% confidence interval
[CI]: [1.08, 1.22]; Edwards et al. 2009). However, as acknowledged by
Edwards et al. (2009), there was substantial heterogeneity among the studies
that investigated the effect of nonmonetary incentives, so it may not be appro-
priate to combine them. Combining these studies also makes it difficult to
determine what specific kinds of nonmonetary incentives are effective.
The studies that have investigated the effect of lottery scratch tickets on
response have generally had null findings (Finsen and Storeheier 2006;
Harris, Khoo, et al. 2008; Kalantar and Talley 1999; Koloski et al. 2001;
Ward et al. 1996; Wenemark et al. 2010; Whiteman et al. 2003), with only
one study showing a significant increase in the likelihood of response
(Robertson et al. 2005). Several studies have shown a borderline, but non-
significant, increase in response (Brennan et al. 1993; Kalantar and Talley
1999; Ward et al. 1996; Whiteman et al. 2003), which suggests that they
may have had insufficient power to detect a significant difference. The
published research about the effect of donation offers on response has
shown mixed results, with some studies showing no effect or a decrease
in response (Gattellari and Ward 2001; Gendall and Healey 2008; Hubbard
and Little 1988; Skinner et al. 1984), and others showing an increase in
response (Brennan et al. 1993; Deehan et al. 1997; Faria and Dickinson
Boyle et al. 113
1992; Furse and Stewart 1982; Gendall and Healey 2008; Robertson and
Bellenger 1978; Warriner and Goyder 1996). Overall, there is limited
research concerning the effectiveness of lottery scratch tickets and donation
offers.
We conducted two studies to investigate the effect of different types of
nonmonetary incentives on response fraction in the Western Australian
Bowel Health Study (WABOHS), a case–control study of the genetic and
environmental causes of colorectal cancer. The aims of the first study were
to determine whether (1) lottery scratch tickets given at the time of invita-
tion increase response fraction and (2) lottery scratch tickets given at the
same times as the study instruments increase the likelihood that participants
will complete and return them.
For the second study, we modified the incentive to be one of three: a lot-
tery scratch ticket, a donation to The Cancer Council Western Australia, and
a lottery scratch ticket plus a donation. We wanted to compare these incen-
tives as it was hypothesized that a donation to a cancer organization might
be more acceptable than a lottery ticket that could be perceived as having an
association with gambling. We also wanted to determine whether the com-
bination of a personal incentive (a lottery scratch ticket) and an altruistic
incentive (a charitable donation) increased response more than either of
these incentives alone. So, the aim of the second study was to (3) investigate
if a donation offer, or both a donation offer and a lottery scratch ticket,
increased response fraction more than a lottery scratch ticket alone.
We also performed a meta-analysis to determine whether lottery scratch
tickets or donation offers increase response to postal questionnaires.
Method
The two studies were part of a larger study, the WABOHS, the methodology
of which has been described elsewhere (Iacopetta et al. 2009). The
WABOHS was a case–control study of colorectal cancer that took place
between 2005 and 2007 in Western Australia. Cases studied involved indi-
viduals with colorectal cancer who were notified to the Western Australian
Cancer Registry. Age- and sex-matched controls were selected randomly
from the electoral roll of Western Australia. Registration on the electoral
roll is compulsory in Australia, and it is considered virtually complete.
Fifty-eight percent of eligible cases and 46% of eligible controls partici-
pated in the WABOHS.
Ethics approval for both substudies was obtained from the University
of Western Australia Human Research Ethics Committee and the
114 Field Methods 24(1)
Confidentiality of Health Information Committee within the Western
Australian Department of Health.
Study 1
In February 2007, 308 controls (aged between 40 and 79) were randomly
selected from the electoral roll and invited to participate in the WABOHS.
The participants received an invitation letter, an information sheet about the
study, a consent form, and a reply-paid envelope. Using block randomiza-
tion, the controls were allocated into one of two groups at the time of
invitation—Group B received a $2 lottery scratch ticket with their invita-
tion; Group A did not. Nonresponders were sent a reminder letter 3 weeks
after the initial invitation.
Participants who consented to take part in the WABOHS were then sent
a study pack that consisted of two questionnaires and a DNA self-extraction
kit. These participants were randomized further into three groups when sent
their study packs, ignoring their initial allocation to Group A or B (see
Figure 1). Group 0 did not get a lottery scratch ticket, Group 1 received a
$2 lottery scratch ticket, and Group 2 was promised a $2 lottery scratch
ticket on return of their completed study pack. Nonresponders in all three
groups were sent a reminder card after 3 weeks and a replacement study
pack after 5 weeks. The consent forms of seven consenting participants
were received several months after the first study had concluded—these
participants were included in the overall consent and response fractions
(Table 1) but were not included in the second part of the study (Table 2).
Study 2
In June 2007, an additional 300 controls (aged between 40 and 79) were
randomly selected from the electoral roll and invited to participate in the
WABOHS. In this study, the participants were allocated (using block
randomization) into one of the three groups at the time of invitation
(Figure 2). Group X received a $2 lottery scratch ticket with their invitation,
Group Y were told that $2 would be donated to The Cancer Council West-
ern Australia if they returned their consent form (regardless of whether or
not they agreed to take part in the WABOHS), and Group Z received both
a $2 lottery scratch ticket and the donation offer. Nonresponders in all three
groups were sent a reminder letter 3 weeks after the initial invitation. Con-
senting participants were sent a study pack to complete but did not receive
any incentives at the second stage. Participants who did not return their
Boyle et al. 115
308
part
icip
ants
ran
dom
ly
sele
cted
fro
m th
e el
ecto
ral r
oll
Gro
up A
: 154
par
ticip
ants
sen
t inv
itatio
n w
itho
ut in
cent
ive
Gro
up B
: 154
par
ticip
ants
sen
t inv
itatio
n w
ith
$2 s
crat
ch ti
cket
57pa
rtic
ipan
tsdi
d no
t con
sent
66 p
artic
ipan
ts
did
not c
onse
nt93
part
icip
ants
agr
eed
to
part
icip
ate
81pa
rtic
ipan
ts a
gree
dto
par
ticip
ate
Gro
up 0
: 27
part
icip
ants
sen
t st
udy
pack
w
itho
ut in
cent
ive
Gro
up 2
: 29
part
icip
ants
pr
omis
ed $
2 sc
ratc
h tic
ket
on r
etur
n of
com
plet
ed
stud
y pa
ck
Gro
up 1
: 25
part
icip
ants
sen
t st
udy
pack
with
$2
scr
atch
tick
et
Gro
up 0
: 31
part
icip
ants
sen
t st
udy
pack
w
itho
ut in
cent
ive
Gro
up 2
: 30
part
icip
ants
pr
omis
ed $
2 sc
ratc
h tic
keto
n re
turn
of
com
plet
ed s
tudy
pack
Gro
up 1
: 32
part
icip
ants
sen
t st
udy
pack
with
$2
scr
atch
tick
et
3 pa
rtic
ipan
ts
inel
igib
le1
part
icip
ant
inel
igib
le
4 pa
rtic
ipan
ts a
gree
d to
pa
rtic
ipat
e la
te3
part
icip
ants
agr
eed
to
part
icip
ate
late
Figure 1. Design of study 1.
116 Field Methods 24(1)
study pack were sent a reminder card after 3 weeks and a replacement study
pack after 5 weeks.
Statistical Analysis
Consent fractions, response fractions, and risk ratios were generated using
the statistical package Stata 10.0 (StataCorp., College Station, TX). Consent
fraction refers to the percentage of all eligible invited participants who indi-
cated on their returned consent form that they were willing to take part in
the study. Response fraction refers to the percentage of all eligible invited
participants who returned a completed study pack. Risk ratios were gener-
ated using a modified Poisson regression approach (Zou 2004). Effect
Table 1. Response and Consent Fractions among Participants Receiving Either aLottery Scratch Ticket or No-Incentive at the Time of Invitation (N ¼ 304)
NumberResponding Percentage
RiskRatio 95% CI
Consent fraction before reminderGroup A. No incentive (n ¼ 151) 62 41.1 1.00 —Group B. Scratch ticket (n ¼ 153) 82 53.6 1.31 [1.02, 1.66]
Consent fraction after reminderGroup A 85 56.3 1.00 —Group B 96 62.7 1.11 [0.93, 1.34]
Consented and completed study pack (response fraction)Group A 70 46.4 1.00 —Group B 88 57.5 1.24 [1.00, 1.55]
Table 2. Study Pack Return among Groups that were Given, Promised, or NotGiven an Incentive with the Study Pack (N ¼ 174)
NumberResponding Percentage
RiskRatio 95% CI
Group 0. No incentive with studypack (n ¼ 58)
50 86.2 1.00 —
Group 1. Incentive with study pack(n ¼ 57)
49 86.0 1.00 [0.86, 1.16]
Group 2. Promised incentive onreceipt of completed study pack(n ¼ 59)
56 94.9 1.10 [0.98, 1.24]
Boyle et al. 117
300
part
icip
ants
ran
dom
ly
sele
cted
fro
m th
e el
ecto
ral r
oll
Gro
up X
: 100
part
icip
ants
sen
t in
vita
tion
wit
h $2
scr
atch
tick
etG
roup
Z: 1
00pa
rtic
ipan
ts s
ent
invi
tatio
n w
ith
$2 s
crat
ch ti
cket
an
da
$2 d
onat
ion
offe
r
48 p
artic
ipan
tsdi
d no
t con
sent
55 p
artic
ipan
ts
did
not c
onse
nt51
part
icip
ants
agr
eed
to
part
icip
ate
45pa
rtic
ipan
ts a
gree
dto
par
ticip
ate
0 pa
rtic
ipan
ts
inel
igib
le1
part
icip
ant
inel
igib
le
Gro
up Y
: 100
par
ticip
ants
sen
t in
vita
tion
wit
h a
$2 d
onat
ion
offe
r
47pa
rtic
ipan
ts a
gree
dto
par
ticip
ate
50pa
rtic
ipan
ts
did
not c
onse
nt
3 pa
rtic
ipan
ts
inel
igib
le
Figure 2. Design of study 2.
118 Field Methods 24(1)
modification by age, sex, or invitation incentive group (Study 1b) was
examined using postestimation Wald’s chi-square tests.
Meta-Analyses
A systematic search of Medline, PsychInfo, Cochrane Controlled Trials
Register, Embase, Institute for Scientific Information (ISI), Web of
Knowledge, Proquest 5000, and Scopus (to June 2010) was conducted
to identify studies that had investigated the effect of scratch lottery tick-
ets or donation offers on response. Only studies that compared the use
of lottery scratch tickets or donation offers with a no monetary or non-
monetary incentive control group were considered. Only studies that
involved postal surveys/questionnaires were included; studies that inves-
tigated the effect of these incentives on response to web-based question-
naires or telephone surveys were not considered. Studies from any
populations were considered, as long as they were published in English
in a peer-reviewed journal.
The following search strategy was used for lottery scratch ticket articles:
1. questionnair* or survey* or data collection
2. respon* or return*
3. lottery or instant or scratch*
4. ticket or card
5. 1 & 2 & 3 & 4
The following search strategy was used for donation offer articles:
1. questionnair* or survey* or data collection
2. respon* or return*
3. charit* and donat*
4. 1 & 2 & 3
The lottery scratch ticket search resulted in a total of 78 articles. Of these,
57 were not considered as they were not related to response to question-
naires. Of the remaining 21 articles, 13 were not included in the meta-
analysis as they did not involve lottery scratch tickets or did not have a
no-incentive control group. The donation offer search resulted in a total
of 156 articles. Of these, 147 were not considered as they were not related
to response to questionnaires. Of the remaining nine articles, two were not
included in the meta-analysis as they did not involve donation offers or did
Boyle et al. 119
not have a no-incentive control group. The recent Cochrane review con-
cerning the use of incentives in mailed and online questionnaires was also
searched (Edwards et al. 2009), resulting in one additional study for
the lottery scratch ticket meta-analysis and two additional studies for the
donation offer meta-analysis. A search of the reference lists of all the
eligible articles did not find any additional studies. Three further studies
were added to the donation offer meta-analysis during the review process
of this article.
In total, 9 studies (including the present study) were included in the lot-
tery scratch ticket meta-analysis, and 12 studies were included in the dona-
tion offer meta-analysis. The characteristics of these studies can be found in
Tables 3 and 4.
If a study had more than one incentive group level, these levels were
combined to produce a dichotomous result (i.e., incentive groups vs. no-
incentive groups). The outcome was the proportion of returned question-
naires after all mailings. As incentives given unconditionally have been
shown to have significantly greater effect on response than those given
conditionally (Edwards et al. 2009), studies that used conditional lottery
scratch tickets were analyzed separately than those that used unconditional
lottery scratch tickets.
Table 3. Response and Consent Fractions among Participants Receiving Eithera Lottery Scratch Ticket, a Donation Offer, or Both, at the Time of Invitation (N¼ 296)
NumberResponding Percentage
RiskRatio 95% CI
Consent fraction before reminderGroup X. Scratch ticket only
(n ¼ 100)37 37.0 1.00 —
Group Y. Donation only (n ¼ 97) 32 33.0 0.89 [0.61, 1.31]Group Z. Donation/scratch ticket
(n ¼ 99)39 39.4 1.06 [0.75, 1.52]
Consent fraction after reminderGroup X 45 45.0 1.00 —Group Y 47 48.5 1.08 [0.8, 1.45]Group Z 48 48.5 1.08 [0.8, 1.45]
Consented and completed study pack (response fraction)Group X 41 41.0 1.00 —Group Y 44 45.4 1.11 [0.8, 1.52]Group Z 41 41.4 1.01 [0.72, 1.41]
120 Field Methods 24(1)
Tab
le4.
Char
acte
rist
ics
ofth
eSt
udie
sIn
cluded
inth
eLo
tter
ySc
ratc
hT
icke
tM
eta-
Anal
ysis
Firs
tA
uth
or,
Yea
rPar
tici
pan
ts,Lo
cation
Surv
eyT
opic
Ince
ntive
Gro
ups
(and
Num
ber
of
Par
tici
pan
ts)
Use
din
This
Anal
ysis
Qual
ity
ofA
lloca
-tion
Conce
alm
ent
Bre
nnan
etal
.1993
Dai
ryan
dbee
ffa
rmer
sin
New
Zea
land
Use
ofm
iner
alsu
pple
men
ts1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
101)
Uncl
eara
2.G
iven
one
NZ
$1
lott
ery
scra
tch
tick
et(N¼
108)
War
det
al.
1996
Pat
ients
from
age
ner
alpra
ctic
ein
Sydney
,A
ust
ralia
Hea
lth,ri
skfa
ctors
,pat
ient
satisf
action
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
112)
Uncl
eara
2.G
iven
one
AU
$1
lott
ery
scra
tch
tick
et(N¼
119)
Kal
anta
ran
dT
alle
y1999
Res
iden
tsofW
este
rnSy
dney
,A
ust
ralia
Hea
lth
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
220)
Adeq
uat
ea
2.G
iven
one
AU
$1
lott
ery
scra
tch
tick
et(N¼
220)
Kolo
skiet
al.
2001
Res
iden
tsofPen
rith
,A
ust
ralia
Gas
troin
test
inal
dis
ord
ers
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
252)
Uncl
eara
2.G
iven
one
AU
$1
lott
ery
scra
tch
tick
et(N¼
248)
Whitem
anet
al.2003
Mid
life
wom
enin
Bal
tim
ore
,U
SAH
ealth
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
600)
Adeq
uat
ea
2.G
iven
one
US$
1lo
tter
ysc
ratc
htick
et(N¼
1,2
00)
Rober
tson
etal
.2005
Clin
ical
pra
ctic
esofge
ner
alpra
cti-
tioner
san
dsp
ecia
lists
inA
ust
ralia
Upta
keofnew
med
icat
ions
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
469)
Adeq
uat
ea
2.G
iven
one
AU
$2
lott
ery
scra
tch
tick
et(N¼
469)
(con
tinue
d)
121
Tab
le4
(co
nti
nu
ed
)
Firs
tA
uth
or,
Yea
rPar
tici
pan
ts,Lo
cation
Surv
eyT
opic
Ince
ntive
Gro
ups
(and
Num
ber
of
Par
tici
pan
ts)
Use
din
This
Anal
ysis
Qual
ity
ofA
lloca
-tion
Conce
alm
ent
Finse
nan
dSt
ore
hei
er2006
Res
iden
tsofN
orw
ayH
isto
ryofm
edic
aloper
atio
ns
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
500)
Inad
equat
ea
2.G
iven
one
or
two
NO
K20
lott
ery
scra
tch
tick
ets
(N¼
500)
3.Pro
mis
edone
NO
K20
lott
ery
scra
tch
tick
et(N¼
250)
Har
ris,
Khoo,
etal
.2008
Maj
or
trau
ma
pat
ients
ata
met
ropol-
itan
trau
ma
cente
r,A
ust
ralia
Gen
eral
hea
lth
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
329)
Uncl
ear
2.Pro
mis
edone
AU
$4
lott
ery
scra
tch
tick
et(N¼
343)
Wen
emar
ket
al.2010
Par
ents
ofch
ildre
nw
ith
cance
r,Sw
eden
Stre
ss1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
150)
Uncl
ear
2.Pro
mis
edone
or
two
Skr1
0lo
tter
ysc
ratc
htick
ets
(N¼
300)
Boyl
eet
al.,
2012
Res
iden
tsofW
este
rnA
ust
ralia
Colo
rect
alca
nce
rri
skfa
ctors
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
151)
Adeq
uat
e
2.G
iven
one
AU
$2
lott
ery
scra
tch
tick
et(N¼
153)
Not
e:a Fr
om
Edw
ards
etal
.(2
009).
122
The command metan in the statistical package Stata 10.0 (StataCorp,
College Station, TX) was used to conduct random-effects meta-analyses
(DerSimonian and Laird 1986).
Results
Study 1
Of the 308 controls invited in the first study, 4 were not contactable due to
incorrect addresses. Group A (no incentive) had a mean age of 62.1 years
(range ¼ 40–79 years) and Group B (lottery scratch ticket) had a mean age
of 62.5 years (range ¼ 42–79 years). The proportion of females in each
group was 38.4% and 37.9%, respectively. Of the eligible 304 controls,
181 (144 before the reminder letter and 37 after the reminder letter) con-
sented to take part in the WABOHS (consent fraction ¼ 59.5%), with
158 completing and returning their study pack (response fraction ¼52.0%). The reminder letter increased the consent fraction from 47.4% to
59.5%.
Participants who received a lottery scratch ticket with their invitation
(Group B) were 1.24 times (95% CI [1.00, 1.55]) more likely to take part
in the study than participants who did not receive an incentive (Table 1).
Participants who received a lottery scratch ticket with their invitation were
1.31 times (95% CI [1.02, 1.66]) more likely to consent to take part in the
study without needing a reminder than those who did not receive an incen-
tive. There was no significant difference in consent fractions between the
two groups following the reminder letter. There were no significant sex
or age differences in terms of the effect of the incentive.
There were no significant differences in the likelihood of participants
completing and returning their study pack between the three study pack
incentive groups (Table 2). The invitation incentive group did not signifi-
cantly modify the effect of the study pack incentive (the response fractions
of the six individual groups can be found in Table 5).
Study 2
Of the 300 controls invited in the second study, 4 were not contactable due
to incorrect addresses. Group X (lottery scratch ticket only) had a mean age
of 58.6 years (range ¼ 40–79 years), Group Y (donation only) had a mean
age of 59.7 years (range¼ 40–79 years), and Group Z (both incentives) had
a mean age of 58.0 (range ¼ 40–79 years). The proportion of females in
each group was 38%, 44.4%, and 41.2%, respectively. Of the eligible 296
Boyle et al. 123
controls, 140 (108 before the reminder letter and 32 after the reminder letter)
consented to take part in the WABOHS (consent fraction ¼ 47.3%), with
126 completing and returning their study pack (response fraction ¼ 42.6%).
The reminder letter increased the consent fraction from 36.5% to 47.3%.
The highest response fraction was seen in Group Y (donation only);
however, there were no significant differences in consent and response frac-
tions between the three different incentive groups (see Table 3). There were
no significant sex or age differences in terms of the effect of the incentive.
Meta-Analyses
The characteristics of the studies included in the meta-analyses can be
found in Tables 4 and 6. As shown in Figure 3, the results of the random-
effects meta-analyses show that lottery scratch tickets given uncondition-
ally significantly increase the likelihood of response by 9% (risk ratio
[RR] ¼ 1.09, 95% CI [1.02, 1.16]), compared with a no-incentive control
group. Lottery scratch tickets given conditionally appear to have no effect
on response (RR ¼ 0.97, 95% CI [0.91, 1.04]). There was no significant
Table 5. Study Pack Return among Groups that Were Given or Not Given anIncentive with the Invitation and Were then Given, Promised, or Not Given an Incen-tive with the Study Pack (N ¼ 174)
NumberResponding Percentage
RiskRatio 95% CI
Group A. No incentive with invitationGroup 0. No incentive with studypack (n ¼ 27)
20 74.1 1.00 —
Group 1. Incentive with studypack (n ¼ 25)
21 84.0 1.13 [0.86, 1.50]
Group 2. Promised incentive onreceipt of completed study pack(n ¼ 29)
28 96.6 1.30 [1.03, 1.65]
Group B. Incentive with invitationGroup 0. No incentive with studypack (n ¼ 31)
30 96.8 1.31 [1.04, 1.65]
Group 1. Incentive with studypack (n ¼ 32)
28 87.5 1.18 [0.91, 1.53]
Group 2. Promised incentive onreceipt of completed study pack(n ¼ 30)
28 93.3 1.26 [0.99, 1.61]
124 Field Methods 24(1)
Tab
le6.
Char
acte
rist
ics
ofth
eSt
udie
sIn
cluded
inth
eD
onat
ion
Offer
Met
a-A
nal
ysis
Firs
tA
uth
or,
Yea
rPar
tici
pan
ts,Lo
cation
Surv
eyT
opic
Ince
ntive
Gro
ups
(and
Num
ber
of
Par
tici
pan
ts)
Use
din
This
Anal
ysis
Qual
ity
ofA
lloca
-tion
Conce
alm
ent
Rober
tson
and
Bel
lenge
r1978
Res
iden
tsofD
enve
r,U
SAN
ot
spec
ified
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
150)
Uncl
eara
2.U
S$1
contr
ibution
toch
arity
(N¼
150)
Furs
ean
dSt
ewar
t1982
Mic
row
ave
ove
now
ner
s,U
SAN
ot
spec
ified
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
100)
Uncl
eara
2.U
S$1
contr
ibution
toch
arity
(N¼
100)
Skin
ner
etal
.1984
Mar
keting
pro
fess
ors
inC
anad
aA
nin
troduct
ory
mar
keting
textb
ook
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
60)
Uncl
eara
2.C
A$1
contr
ibution
toch
arity
(N¼
60)
Hubbar
dan
dLi
ttle
1988
Res
iden
tsofa
mid
wes
tern
met
ropolit
anar
ea,U
SASa
tisf
action
with
finan
cial
serv
ices
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
400)
Uncl
eara
2.U
S$1
contr
ibution
toch
arity
(N¼
400)
Fari
aan
dD
icki
nso
n1992
Busi
nes
scu
stom
ers
ofa
maj
or
man
ufa
cture
r,C
anad
aN
ot
spec
ified
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
500)
Adeq
uat
ea
2.C
A$2
contr
ibution
toch
arity
(N¼
1,0
00)
Bre
nnan
etal
.1993
Res
iden
tsofN
ewZ
eala
nd
Att
itudes
tow
ard
soci
alin
equal
ity
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
452)
Uncl
eara
2.N
Z$1
contr
ibution
toch
arity
(N¼
478)
(con
tinue
d)
125
Tab
le6
(co
nti
nu
ed
)
Firs
tA
uth
or,
Yea
rPar
tici
pan
ts,Lo
cation
Surv
eyT
opic
Ince
ntive
Gro
ups
(and
Num
ber
of
Par
tici
pan
ts)
Use
din
This
Anal
ysis
Qual
ity
ofA
lloca
-tion
Conce
alm
ent
War
riner
and
Goyd
er1996
Res
iden
tsofth
eG
rand
Riv
erW
ater
shed
regi
on,O
nta
rio,
Can
ada
Envi
ronm
enta
lis
sues
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
110)
Inad
equat
ea
2.C
A$2,$5
or
$10
contr
ibution
toch
arity
(N¼
139)
Dee
han
etal
.1997
Gen
eral
pra
ctitio
ner
sin
Engl
and
and
Wal
esW
ork
with
alco
hol-
abusi
ng
pat
ients
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
1,1
88)
Uncl
eara
2.G
B£5
or
£10
contr
ibution
toch
arity
(N¼
1,1
85)
Gat
tella
rian
dW
ard
2001
Act
ive
Fello
ws
ofth
eR
oya
lA
ust
rala
sian
Colle
geof
Surg
eons
Clin
ical
pra
ctic
egu
idel
ines
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
111)
Adeq
uat
ea
2.A
U$10
contr
ibution
toth
eR
AC
S(N¼
108)
Gen
dal
lan
dH
eale
y2008
Res
iden
tsofN
ewZ
eala
nd
Imm
igra
tion
inN
ewZ
eala
nd
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
200)
Uncl
ear
2.N
Z$1
contr
ibution
toch
arity
(N¼
200)
Gen
dal
lan
dH
eale
y2008
Res
iden
tsofN
ewZ
eala
nd
Adve
rtis
ing
Reg
ula
tion
1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
500)
Uncl
ear
2.N
Z$1
contr
ibution
toch
arity
(N¼
500)
Gen
dal
lan
dH
eale
y2010
Res
iden
tsofN
ewZ
eala
nd
Rel
igio
n1.N
om
onet
ary
or
nonm
onet
ary
ince
ntive
(N¼
406)
Uncl
ear
2.N
Z$1,$2
or
$5
contr
ibution
toch
arity
(N¼
1,5
47)
Not
e:a Fr
om
Edw
ards
etal
.(2
009).
126
heterogeneity among the studies that examined the effect of lottery scratch
tickets given unconditioanlly (p ¼ .128) or conditionally (p ¼ .555).
Compared with a no-incentive control group, donation offers may
increase the likelihood of response by 4% (RR ¼ 1.04, 95% CI [0.96,
1.14]), although this result was not statistically significant (Figure 3). There
was significant heterogeneity among the studies that examined the effect of
donation offers on response (p < .001). Stratifying the studies by question-
naire topic (commercial or social/health) and study location (Australasia,
North America, or Europe) did not account for the significant heterogeneity,
nor did it reveal any meaningful differences between the effect sizes.
A sensitivity analysis, in which each study was omitted from the
meta-analysis one at a time, showed no notable impact of any study on the
effect size.
Figure 3. Meta-analyses and forest plot of studies that have investigated the effectof lottery scratch tickets or donation offers on response to mailed questionnaires.
Boyle et al. 127
Discussion
The results of the first study and the meta-analysis suggest that lottery
scratch tickets, when given unconditionally, provide a modest increase in
response to mailed questionnaires. In the first study, participants who
received a lottery scratch ticket with their invitation were 1.24 times more
likely to take part in the study than participants who did not receive an
incentive, although this increase just failed to reach statistical significance.
The results of the meta-analysis show that, compared with a no-incentive
control group, lottery scratch tickets given unconditionally increase the
likelihood of a participant responding by 9%. The meta-analysis also sug-
gests that lottery scratch tickets given conditionally do not appear to
increase response, a finding that confirms incentives given unconditionally
are more effective than those given conditionally (Edwards et al. 2009).
In our first study, lottery scratch tickets significantly increased the likeli-
hood of participants consenting before the reminder letter. This finding is con-
sistent with the results of other studies (Kalantar and Talley 1999; Robertson
et al. 2005), suggesting that if researchers are not planning to follow up non-
responders, using a lottery scratch ticket may be an effective method to
increase response. The increased response to the first mailing also reduces the
costs and resources associated with the sending of reminders, which offsets the
cost of the lottery scratch tickets to a certain extent (Kalantar and Talley 1999).
It is important to note, however, that follow-up contact has been shown to be a
very effective method of increasing response fraction (Edwards et al. 2009),
and the findings of this study—in which a reminder letter increased the
response fraction from 47.4% to 59.5% in the first study and from 36.5% to
47.3% in the second study—support this.
The results of the first study also indicate that giving or promising a lot-
tery scratch ticket with the study instruments does not significantly increase
the likelihood that participants will complete and return them.
The results of the second study suggest that lottery scratch tickets and
donation offers have a similar overall effect on consent and response frac-
tions. This suggests that incentives that have an altruistic benefit (i.e., dona-
tion offers) have a similar effect to incentives that may lead to personal
benefit (i.e., lottery scratch tickets). However, in the meta-analyses, we
found that lottery scratch tickets may have a greater effect on response than
donation offers. Lottery scratch tickets given unconditionally increase the
likelihood of response by 9%, while donation offers increase the chance
of response by 4%. The 4% increase was not statistically significant, and
there was significant heterogeneity among the studies that have investigated
128 Field Methods 24(1)
the effect of donation offers on response, so the effect of donation offers on
response remains unclear.
The fact that the two studies were both done within a larger study (the
WABOHS) led to some limitations. The number of participants in both the
first and the second studies, particularly in the final three groups in the first
study, limited our ability to draw conclusions; however, the total sample
size was constrained by the number of participants invited to take part in
the WABOHS at that time. A no-incentive control group in the second study
may have made the effect of different types of nonmonetary incentives
more clear. The generalizability of the results of the two studies may be lim-
ited, as both were conducted with quite homogeneous samples in a health
research setting. Likewise, all the studies in the lottery scratch tickets
meta-analysis were conducted within a health or social research setting,
so the results may not be generalizable to other research settings (e.g., mar-
ket research).
Despite using several techniques that have been shown to increase
response fraction—including personalized invitation letters, university
sponsorship, supplying a reply-paid envelope, reminder letters, promising
to supply the results of the study, and using a nonmonetary incentive, and
reminders (Edwards et al. 2009)—the final response fraction among con-
trols in the entire WABOHS was a modest 46%. Given that the nonmone-
tary incentives used in this study appear to result in only a small increase
in the likelihood of response, it is important that the effect of other types of
incentives on response is investigated. With response fractions in epide-
miological studies declining (Morton et al. 2006), and considering that
even small amounts of nonresponse bias can lead to inflation or attenua-
tion of the true effect (Harris, Levy, et al. 2008), increasing response is an
important issue.
Acknowledgments
Many thanks to Cassandra Clayforth, Clare Tran, Beatriz Cuesta-Briand,
and Kieran McCaul for their contributions to the two studies. The authors
also thank the four reviewers of this article for their thoughtful and con-
structive comments. Lin Fritschi is supported by an NHMRC Fellowship.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the
research, authorship, and/or publication of this article.
Boyle et al. 129
Funding
The author(s) disclosed receipt of the following financial support for the
research, authorship and/or publication of this article: The Western Austra-
lian Bowel Health Study was funded by the National Health and Medical
Research Council (Grant Number 353568). The funding source had no
involvement in either of these studies.
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