Abstract
Under certain circumstances it is possible to apply latent structure models to estimate ζ, the proportion of skills an examinee has acquired among a domain of skills and to estimate β, the probability of guessing the correct response given that the examinee does not know. Models have also been formulated in which ζ represents the proportion of examinees who know a specific skill and again β is the probability of guessing. Macready and Dayton (1976) have used these models to determine the number of items required in deciding whether an examinee has acquired a particular skill and Wilcox (1979) has applied these models to arrive at a formula score which allows guessing to vary over the population of examinees. In this paper we examine a technical problem associated with estimating β and we also indicate situations for which this problem does not occur. It is shown, however, that this problem does not apply when using Wilcox's formula score. In addition, some new, explicit, maxi mum likelihood estimates of ζ and β are derived which may be applied when items are hierarchically related.
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