Reply to Glenn (Hout M. - Knoke D., 1976)

7/27/2019 Reply to Glenn (Hout M. - Knoke D., 1976)

1/5

Reply to GlennAuthor(s): David Knoke and Michael HoutSource: American Sociological Review, Vol. 41, No. 5 (Oct., 1976), pp. 905-908Published by: American Sociological AssociationStable URL: http://www.jstor.org/stable/2094740 .

Accessed: 25/07/2013 14:15

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of

content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms

of scholarship. For more information about JSTOR, please contact [email protected].

.

American Sociological Association is collaborating with JSTOR to digitize, preserve and extend access to

American Sociological Review.

http://www.jstor.org

This content downloaded from 186.18.32.91 on Thu, 25 Jul 2013 14:15:08 PMAll use subject to JSTOR Terms and Conditions
http://www.jstor.org/action/showPublisher?publisherCode=asahttp://www.jstor.org/stable/2094740?origin=JSTOR-pdfhttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/stable/2094740?origin=JSTOR-pdfhttp://www.jstor.org/action/showPublisher?publisherCode=asa


2/5

COMMENTS 905to be conceptually inadequate for the broadrange of "'nondemographic" variables. But inso doing, he makes no comparisons withalternative models and he does not establishhis conclusion in the context of specific sub-stantive problems. Moreover, in rejecting ad-ditive models, Glenn totally ignores the cri-terion of empirical adequacy. Thus, in failingto relate additive formulations to other formu-lations, either conceptually or empirically,Glenn ignores the purpose of models.Glenn's third point is that the results ofthose cohort analyses affected by the problemof estimability are necessarily tentative. Weagree, but the point is hardly unique to cohortanalyses. The results of all modeling effortsare tentative in the sense that they rest ontheory and assumptions and run the risk ofbeing discarded in favor of results based on acompetitive modeling effort using differenttheory and assumptions. What deserves spe-cial emphasis here is that in models of the sortconsidered in our article, age, period and co-hort are proxies for unmeasured mechanismsor variables. If these mechanisms or vari-ables were measured and available for anal-ysis, the estimability problem dealt with inour paper either would not occur or wouldbe different. For example, if cohort size isheld to be the variable which causes cohortdifferentiation in the context of a particularsubstantive problem, then, if size measure-ments can be constructed, it is unnecessary toinclude cohorts as such in the specificationbecause the preferred variable is available.Under circumstances like this the results ofcohort analysis become less tentative, sincethe estimability problem as we described it iseliminated. The replacement of proxies by thevariables they index is a universal goal ofresearch.In conclusion, we reiterate a point made inour article. Specifications of the kind we dealtwith are not universally appropriate or desira-ble. Cohort analysis can take many forms.Whatever the approach the analyst thinkspromising, care should be taken to develop amodel which is sufficiently formal to enabledetermination of the necessity of estimabilityrestrictions. Such restrictions require theo-retical and substantive justification.

William M. MasonKaren Oppenheim MasonUniversity of MichiganH. H. WinsboroughUniversity of Wisconsin, Madison

In our original article, "Some MethodologicalIssues in Cohort Analysis of Archival Data"

(ASR April, 1973), equation (2), page 246,should read: YJ =,+ ,81Pryj +Sk+ E;J.REFERENCES

Greenberg, B. G., J. J. Wright, C. G. Sheps1950 "A technique for analyzing some factorsaffecting the incidence of syphilis."Journal of the American Statistical As-sociation 251:373-99.Hall, R. E.1971 "The measurement of quality changefrom vintage price data." Pp. 240-71in Z. Griliches (ed.), Price Indexes andQuality Changes. Cambridge: HarvardUniversity Press.Winsborough, H. H.1975 "Age, period, cohort, and educationeffects on earnings by race-an experi-ment with a sequence of cross-sectionalsurveys." Pp. 201-17 in K. Land andS. Spilerman (eds.), Social IndicatorModels. New York: Russell Sage.

REPLY TO GLENN *We welcome this opportunity to clarifyexplicitly our application of the cohort-age-period model to our studies of party identifi-

cation and voting turnout in the United States(Knoke and Hout, 1974; Hout and Knoke,1975). First, we reanalyze previously pub-lished cohort data to demonstrate the reason-ableness of our assumption of constant cohorteffects on party identification. Next, weclarify some of the semantic confusion whichseems to attend the use of the terms "addi-tive" and "interactive" statistical models.Finally, we raise some questions concerningthe ultimate implications of Glenn's sugges-tions for developing a sociological analysis ofcohort behavior.Glenn questions whether our assumptionof constant cohort effects on party identifica-tion within age and period categories is rea-sonable. Here we offer evidence supportingour assumption, based on survey data reportedin Glenn and Hefner (1972), Glenn (1972)and Knoke (1976:ch. 7). Each article reportsthree-way cross-classifications of survey re-spondents by cohort, year of survey and partyidentification (three major party groups). Wesubjected these data to log-linear analyses,fitting to each table several models corre-sponding to different assumptions about therelationships among the three variables.

* We appreciateNorval D. Glenn's commentson severalearlierdraftsof this reply, which havemuch improved the quality and value of thisexchange of views.

http://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsp


3/5

906 AMERICAN SOCIOLOGICAL REVIEWTable 1. x2 Values for Some Log-LinearModels Fitted to Three Cohort-Period-PartyIdentificationCross-Tabulations

Glenn-Hefner Glennb KnokeModel Marginals x2 df x2 df x2 df1 (C)(T)(P) 18,869.9 (132) 1,145.3 (44) 2,941.0 (61)2 (CT)(P) 1,491.5 ( 86) 922.9 -(34) 523.1 (44)3 (CT) (TP) 990.2 ( 74) 597.3 (30) 371.0 (32)4 (CT) (CP) 384.6 ( 74) 348.6 (24) 79.2 (36)5 (CT)(TP)(CP) 122.5 ( 62) 33.9 (20) 33.3 (26)Sample Size (56,235) (29,852) (10,927)

C: Cohort T: Period P: PartyIdentificationa 7 cohorts, 7 periods, 3 parties.b 6 cohorts, 3 periods, 3 parties.e 4 cohorts, 6 periods, 3 parties.

(Where data were missing due to the absenceof a cohort from a time period, we con-strained the entries to fixed zeros, and fitted"quasi-independence" models to the remain-ing cells; see Goodman, 1968.) The resultsare summarized in Table 1.Model 1 fits only the three one-way mar-ginal distributions of each variable, under theassumption that none of the variables areassociated. Of course, this "baseline" modelprovides a poor fit to each data set, but theresulting x2 value may be taken as a measureof the "unexplained variance" to be accountedfor by other models which allow relationshipsamong the variables (see Goodman, 1972:1054). The next three models all show someimprovement in fit by permitting party identi-fication to be associated separately withcohort or year. Finally, model 5 permits alltwo-way marginals to be fitted, testing thehypothesis that only constant relationshipsoccur between cohort, period and party iden-tification.Model 5 asserts that the odds on beingRepublican, Democrat or Independent in agiven cohort are unaffected by the period ofobservation. As the x2 values for model 5show, only the Knoke data attain a significantfit by the usual criterion of a probabilitygreater than .05. But, given the enormous sizeof the samples used by Glenn and Hefner andby Glenn, to expect a statistically significantfit is unreasonable, since x2 values for agiven relationship will increase with samplesize. A better criterion against which to judgethe adequacy of model 5 in each case is theproportion of "unexplained variance" in thebaseline model 1 which is reduced after fittingthe additive model 5. In each case, model 5accounts for more than 97 percent of the x2values for model 1. Even judged againstmodel 2, which permits cohort and period

measures to associate, model 5 still accountsfor more than 90 percent of the baseline x2Thus, we conclude that model 5, which de-picts only two-way relationships betweenvariables in the cohort-period-party tables,provides a highly satisfactory fit to the ob-served data.These results indicate that, contrary toGlenn, the relationship between cohort andparty preference does not vary over periods.Period effects on party identification do occur,as demonstrated by the necessity to includethe (TP) marginal, but these period effectsoperate identically across cohorts. Hence,when shifts in party identification occur overtime, they tend to be as large at older as atyounger age levels. Insofar as conclusionscan be drawn from empirical data from thepost-World War II era, our assumption ofconstant effects among cohort, period and ageon party identification does not seem unrea-sonable.Glenn calls the Mason et al. (1973) cohortmodel, which we used with minor modifica-tion, "additive" in the sense that it assumesage effects are the same at each level ofperiod and cohort, and so forth. Then heacknowledges in a footnote that our modelsare "interactive," in the sense that cohorteffects are an interaction between age andperiod. We suspect that this use of termi-nology is confusing and we want to set therecord straight on the nature of the statisticalmodels we employed.Our models do contain interaction terms,since each age, period and cohort variable isa linear combination of the other two. Indeed,it is interaction that leads to the identificationproblem which motivated the development byMason et al. of procedures to deal with sta-tistical indeterminacy by imposing certainconstraints on the variables. Persons familiar



4/5

COMMENTS 907with the long controversy on the existence ofstatus inconsistency and social mobility effectswill recognize that our models are one of afamily of such interaction-effects models andnot an "additive" effect model in the usualmeaning of. the term (see Duncan, 1966;Knoke, 1973). We feel that the term "addi-tive" should be applied to models which em-ploy only two sets of demographic dummyvariables (for example, age and period) in aregression equation to avoid unnecessary con-fusion.Perhaps Glenn had in mind, as an alterna-tive to our interaction model, a statisticalmodel specifying one dummy variable forevery cell in the age-by-period cross-classifica-tion (see Blau and Duncan, 1967:ch. 11, foran example with social mobility and fertility).We could have fit such a "total" interactionmodel to the data, but to do so would haveproduced uninterpretable results since noparameter could be assigned meaningfullyto age, period or cohort effects.'The interaction model we use specifies onlyone type of cohort effect, which we believeto be most consistent with the theoreticaldefinition of that concept. As explicitly statedin Hout and Knoke (1975:61), our equationassumes that the effect of a given cohort onthe dependent variable remains constant.This specification comes from our theoreticalinterest in the cohort succession hypothesis:"Aggregate changes in societal characteristics,whether in fertility rates or political attitudes,need not involve changes in the attributes ofindividuals. The succession of birth cohortsthrough the population may be sufficient toaccount for aggregate shifts over time if theentering cohorts differ enough from cohortsexiting through death" (Knoke and Hout,1974:701). If the attributes of individualschange during their lifetimes, "demographicmetabolism" is not the only mechanism op-

rating to alter aggregate attributes of thepopulation. By specifying constant cohorteffects, we explicitly limit the causal mech-anism to the cohort succession process.Our assumption of constant cohort effectsis the apparent reason for Glenn's labelingof our model "additive." However, as heacknowledges in a footnote, ours is an inter-action model and, clearly, only one of a largevariety of such interaction models whichmight have been hypothesized. The particularform of the interaction was chosen on theo-retical, not on ad hoc or arbitrary grounds.Clearly, alternative interaction specificationsare possible, although not all will be theo-retically plausible or result in meaningful em-pirical findings. For example, Glenn appearsto argue that cohort effects vary by age and/orperiod; but since the cohort variable is al-ready an interaction term (cohort-period-age), conceptual clarity among the threedemographic dimensions becomes seriouslyblurred when one starts positing second- andthird-order interactions among age, periodand cohort. However, we see a reasonablepossibility that researchers could specifymeaningful interactions other than the typewe chose. Such alternative models could befit to data and the gains in both statistical fitand substantive understanding could be as-sessed. Since alternative specifications arelikely to involve more complex interactionsthan ours, we rightfully must insist that theyprovide a superior explanation to compensatefor the loss of parsimony involved. Until suchrevised model(s) are forthcoming, we standby our results as the most substantively andstatistically plausible explanation of cohortsuccession effects on party identification andvoter turnout which has appeared to date.We appreciate Glenn's exemption of ourefforts from the accusation of "mechanical,atheoretical cohort analysis," and we join himin condemnation of research based on shoddytheoretical work. We are sorry he found ourconclusions stated too "dogmatically," and weherewith acknowledge that our (as anyone's)results will be valid only to the extent thatour assumptions hold. All empirical resultsare ultimately tentative, since there is noproof positive, only disproof. However, webelieve we have further strengthened the casefor the tenability of our interaction model ofthe age, cohort, period effects on party iden-tification and voting turnout. We would wel-come further empirical evidence to the con-trary.Finally, we feel uneasy about the implica-tions we see in Glenn's comment for the de-

1 We did fit our interactionmodel to the cellmeans of the age-by-periodcross-tabulationforboth the party identificationand voting turnoutdata. The proportion of variance in cell meansexplained by our interactionmodel were 56 and66 percent, respectively (df=40). The "total"interaction model, of course, accounts for 100of the cell mean variance, but requires an addi-tional 55 degrees of freedom. On the individuallevel, the age, period and cohort variables addedonly about two and four percent to the R2above that contributed by the social covariates.Thus, the replacement of our constrained inter-action model by the "total" interaction modelonly marginallywould improve the statistical fitof the individual-level data, while resulting insubstantivelychaotic effect parameters.



5/5

908 AMERICAN SOCIOLOGICAL REVIEWvelopment of a sociological analysisof cohortbehavior. His main objection to age-period-cohort analysisas we have employed it seemsto stem from a belief that every cohort experi-ences age and/or period effects in a fashionunique from all other cohorts. Thus, he as-serts, information provided by the behaviorof other cohorts offers no clue to determinethe relative impact of age or period on anycohort.

But if age and/or period effects experiencedby the hypotheticalcohort in his Table 1 are"completelyunique," as he insists, in whatmeaningful sense can they be called effects?(In fact, why stop there; since every indi-vidual experiences his or her life uniquely,should we not insist that no generalizationsacrossindividualsare permissible?)To argue,as Glenn does, that cohort effects ("additiveeffects" in his terms) cannot be found is todestroy the original meaning of the concept."Cohort effects" are restricted to those in-fluenceswhich persistthrough he life cycle ofmembers of the group; thus a "cohorteffect"which changesat every new age and period isa contradiction.Glenn's analysis would leaveus with a juxtapositionof biographical andhistorical situations and, while a valid theo-retical scheme using only these explanatoryconcepts might be possible, such a scheme isneither our objective nor, we infer, Glenn's.For if every cohort is unique in its behaviorat every point in time, then no generaliza-tions can be made and we have no science,even by the weak standardsof contemporarysocial science. We fear that, if Glenn's sug-gestions are taken literally, sociological re-search must forego the aim of discoveringgenerallyvalid relationshipsand settle insteadfor historical description.We personallyfindthat conclusionuntenableand we hope Glenndoes too, but that is where his argumentsseem inescapably o lead. David KnokeIndiana University

Michael HoutUniversity of ArizonaREFERENCES

Blau, Peter M. and Otis Dudley Duncan1967 The American Occupational Structure.New York: Wiley.Duncan, Otis Dudley1966 "Methodological issues in the analysisof social mobility." Pp. 51-.97 in N.Smelser and S. M. Lipset (eds.), SocialStructure and Mobility in EconomicDevelopment. Chicago: Aldine.

Glenn, Norval D.1972 "Sources of the shift to political in-dependence: some evidence from a co-hort analysis."Social Science Quarterly53:494-519.1976 "Cohortanalysts'futile quest: statisticalattempts to separate age, period andcohort effects." American SociologicalReview 41:900-4.Glenn, Norval D. and Ted Hefner1972 "Further evidence on aging and partyidentification." Public Opinion Quar-terly 36:31-47.Goodman, Leo A.1968 "The analysis of cross-classified data:independence, quasi-independence, andinteractions in contingency tables withof without missing entries." Journal of

American Statistical Association 63:1091-131.1972 "A general model for the analysis ofsurveys." American Journal of Soci-ology 77:1035-86.Hout, Michael and David Knoke1975 "Change n voting turnout, 1952-1972."Public Opinion Quarterly39:52-68.Knoke, David1973 "Intergenerationaloccupational mobil-ity and the political partypreferencesofAmerican men." American Journal ofSociology 78:1448-68.1976 Change and Continuity in AmericanPolitics: The Social Bases of PoliticalParties. Baltimore: Johns Hopkins Uni-versity Press.Knoke, David and Michael Hout1974 "Social and demographic factors inAmerican political party affiliations,1952-1972." American Sociological Re-view 39:700-13.Mason, Karen Oppenheim, William M. Mason,H. H. Winsboroughand W. Kenneth Poole1973 "Some methodological issues in cohortanalysisof archivaldata."AmericanSo-ciological Review 38:242-58.

ON THE USE OF ORDINAL DATA INCORRELATION ANALYSIS *(COMMENT ON LABOVITZ,ASR JUNE, 1970)

The practice of treating ordinal data asinterval has been the subject of considerabledebate. A major concern has been the pos-sible sensitivity of statistical results to thechoice of the particular scale used. Theprimary purpose of this paper is to present a

* I wish to thank my colleagues C. R. Plott,John Ferejohn, Morris Fiorina, Robert Bates andMorgan Kousser for their helpful comments andsuggestions.


Reply to Glenn (Hout M. - Knoke D., 1976)

Documents

Transcript of Reply to Glenn (Hout M. - Knoke D., 1976)