Reducing test length through structurally incomplete designs: An illustration.

This paper serves as an illustration of the usefulness of structurally incomplete designs as an approach to reduce the length of educational questionnaires. In structurally incomplete test designs, respondents only fill out a subset of the total item set, while all items are still provided to the whole sample. The scores on the unadministered items are subsequently dealt with by using methods for the estimation of missing data. Two structurally incomplete test designs - one recording two thirds, and the other recording a half of the potentially complete data - were applied to the complete item scores on 8 educational psychology scales. The incomplete item scores were estimated with missing data method Data Augmentation. Complete and estimated test data were compared at the estimates of total scores, reliability, and predictive validity of an external criterion. The reconstructed data yielded estimates that were very close to the values in the complete data. As expected the statistical uncertainty was higher in the design that recorded fewer item scores. It was concluded that the procedure of applying incomplete test designs and subsequently dealing with the missing values is very fruitful for reducing questionnaire length. © 2007 Elsevier Inc. All rights reserved.