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Four different reasons why one will find two factors for a one dimensional concept. Measurement of an attitude towards environmental protection. One can ask questions like: To what extent do you support environmental protection? To what extent are you interested in these problems?
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Four different reasons why one will find two factors for a one dimensional concept
Measurement of an attitude towards environmental protection One can ask questions like: To what extent do you support environmental protection? To what extent are you interested in these problems? Do you give money for these issues? To what extent do you agree that money is given for this goal? Did you even give money for this problem?
The simplex structure • These questions can be ordered • Y1=Interest • Y2=Positive • Y3=Agree with support • Y4=Gave support • Y5= Gives regular support There is an order from weak to strong support
Two factors for unidimensional scales • Guttman (1956) suggested that not all sets of questions should be analyzed by factor analysis • There are data which have been produced by another model than a factor model • In that case one will derive wrong conclusions • In case of a simplex structure one will detect two factors for the one dimensional attitude: a high and a low factor
The factor analysis • With one factor model (N=2220) • chi2 = 1041 df=9 • RMSEA = .23 • Many misspecifications suggested by JRule • With a two factor model • Chi2 = 128 df= 8 • RMSEA = .08 • No misspecifications suggested by JRule
Normal conclusion • Two factor solution: • One for the positive items • One for the negative items • However I think that the model is wrong and that the items are unidimensional
The topic of the seminar • Besides the Simplex model we will present here three other explanations for the two factor solution for a unidimensional set of items • Akos Munnich and Wijbrandt van Schuur will present substantive models • I will present a methodological argument