2Chapter Outline Introduction Controlling for a Third Variable Interpreting Partial TablesPartial Gamma (Gp )
3Chapter Outline Where Do Control Variables Come From? The Limitations of Elaborating Bivariate TablesInterpreting Statistics: Analyzing Civic Engagement
4In This Presentation The logic of the elaboration technique. The construction and interpretation of partial tables.The interpretation of partial measures of association.Direct, spurious, intervening, and interactive relationships.
5IntroductionSocial science research projects are multivariate, virtually by definition.One way to conduct multivariate analysis is to observe the effect of 3rd variables, one at a time, on a bivariate relationship.The elaboration technique extends the analysis of bivariate tables presented in Chapters
6ElaborationTo “elaborate”, we observe how a control variable (Z) affects the relationship between X and Y.To control for a third variable, the bivariate relationship is reconstructed for each value of the control variable.Problem 16.1 will be used to illustrate these procedures.
7Proble m 16.1:Bivariate Table Sample - 50 immigrantsX = length of residenceY = Fluency in EnglishG = .71
8Problem 16.1: Bivariate Table The column %s and G show a strong, positive relationship: fluency increases with length of residence.< 55+Lo20 (80%)10 (40%)30Hi5 (20%)15 (60%)202550
9Problem 16.1Will the relationship between fluency (Y) and length of residence (X) be affected by gender (Z)?To investigate, the bivariate relationship is reconstructed for each value of Z.One partial table shows the relationship between X and Y for men (Z1)and the other shows the relationship for women (Z2).
12Problem 16.1: A Direct Relationship The percentage patterns and G’s for all three tables are essentially the same.Sex (Z) has little effect on the relationship between fluency (Y) and length of residence (X).
13Problem 16.1: A Direct Relationship For both sexes, Y increases with X in about the same way.There seems to be a direct relationship between X and Y.
14X Y Direct Relationships In a direct relationship, the control variable has little effect on the relationship between X and Y.The column %s and gammas in the partial tables are about the same as the bivariate table.This outcome supports the argument that X causes Y.X Y
15Other Possible Relationships Between X, Y, and Z:Spurious relationships:X and Y are not related, both are caused by Z.Intervening relationships:X and Y are not directly related but are linked by Z.
16Other Possible Relationships Between X, Y, and Z:InteractionThe relationship between X and Y changes for each value of Z.We will extend problem 16.1 beyond the text to illustrate these outcomes.
17Spurious Relationships X and Y are not related, both are caused by Z.XZY
18Spurious Relationships Immigrants with relatives who are Americanized (Z) are more fluent (Y) and more likely to stay (X).Length of Res.RelativesFluency
19Spurious Relationships With RelativesG = 0.00< 55+Low30%High70%
20Spurious Relationships No relativesG = 0.00< 55 +Low65%High35%
21Spurious Relationships In a spurious relationship, the gammas in the partial tables are dramatically lower than the gamma in the bivariate table, perhaps even falling to zero.
22Intervening Relationships X and Y and not directly related but are linked by Z.Longer term residents may be more likely to find jobs that require English and be motivated to become fluent.Z X YJobs Length Fluency
23Intervening Relationships Intervening and spurious relationships look the same in the partial tables.Intervening and spurious relationships must be distinguished on logical or theoretical grounds.< 55+Low30%High70%< 55 +Low65%High35%
24InteractionInteraction occurs when the relationship between X and Y changes across the categories of Z.
25Interaction X and Y could only be related for some categories of Z. X and Y could have a positive relationship for one category of Z and a negative one for others.Z1 X Y Z2 0Z1 + X Y Z2 -
26InteractionPerhaps the relationship between fluency and residence is affected by the level of education residents bring with them.
27InteractionWell educated immigrants are more fluent regardless of residence.Less educated immigrants are less fluent regardless of residence.< 55+Low20%High80%< 55 +Low60%High40%
28Partials compared with bivariate Summary: Table 16.5Partials compared with bivariatePatternImplicationNext StepTheory thatX Y isSameDirectDisregard ZSelect another ZSupportedWeakerSpuriousIncorporate ZFocus on relationship between Z and YNot supported
29Partials compared with bivariate Summary: Table 16.5Partials compared with bivariatePatternImplicationNext StepTheory thatX Y isInterveningIncorporate ZFocus on relationship between X, Y, and ZPartially supportedMixedInteractionAnalyze categories of Z