Abortion attitudes, 1984-1987-1988: effects of item order and dimensionality.

The comparability of surveys is often hampered by differences in the item order of presentation. The major focus of the present study was to investigate whether a general item or a specific item at the beginning of the questionnaire would affect the endorsement as well as the scalability of a set of attitude items. By using a quasi-A-B-A experimental design for the six abortion items that appeared in the Edmonton Area Survey for the years 1984, 1987, and 1988, we found that the order of presentation of the items affected dramatically the endorsement of the abortion items. Approval of a general item was considerably higher when asked first than when asked after a specific item. In contrast, it was shown by means of a nonparametric item response theory model (the Mokken scale analysis) that the unidimensionality of the six abortion items was not affected by the manipulations of item order (i.e., the six abortion items measured the same concept in the three surveys). It was concluded that the six items are unidimensional and, therefore, create a single scale to measure the change in abortion attitudes across the three periods.