Browsing by Author "Forsyth, Robert A."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    An examination of the characteristics of unidimensional IRT parameter estimates derived from two-dimensional data
    (1985) Ansley, Timothy N.; Forsyth, Robert A.
    The purpose of this investigation was to study the nature of the item and ability estimates obtained when the modified three-parameter logistic model is used with two-dimensional data. To examine the effects of two-dimensional data on unidimensional parameter estimates, the relative potency of the two dimensions was systematically varied by changing the correlations between the two ability dimensions. Data sets based on correlations of .0, .3, .6, .9, and .95 were generated for each of four combinations of sample size and test length. Also, for each of these four combinations, five unidimensional data sets were simulated for comparison purposes. Relative to the nature of the unidimensional estimates, it was found that the [circumflex a] value seemed best considered as the average of the true a values. The [circumflex b] value seemed best thought of as an overestimate of the true b[subscript 1] values. The [circumflex theta] value seemed best considered as the average of the true ability parameters. Although there was a consistent trend for these relationships to strengthen as the ability dimensions became more highly correlated, there was always a substantial disparity between the magnitudes of these values and of those derived from the unidimensional data. Sample size and test length had very little effect on these relationships.
  • Thumbnail Image
    Item
    A note on "Planning an experiment in the company of measurement error" by Levin and Subkoviak
    (1978) Forsyth, Robert A.
    Levin and Subkoviak (1977) contend that experimenters should consider the reliability of their measures when comparing the power of fixed-effects completely randomized designs with that of randomized block designs. The two major purposes of this note are (1) to show that under the conditions specified by Levin and Subkoviak, it is not necessary to consider the reliabilities when comparing these two designs and (2) to identify certain errors in the illustrative example used by Levin and Subkoviak.
  • Thumbnail Image
    Item
    Some empirical results related to the robustness of the Rasch model
    (1981) Forsyth, Robert A.; Saisangjan, Upatham; Gilmer, Jerry S.
    The primary purpose of this study was to investigate the invariance properties of the Rasch model using data from standardized achievement tests that were not constructed to conform to the Rasch model. The item responses of approximately 3,400 examinees (Grades 9, 10, 11, and 12) to four separately timed sections of the Iowa Tests of Educational Development were analyzed. The results indicated that the Rasch model does yield reasonably invariant item parameter and ability parameter estimates for different tests and different examinee groups, even though the assumptions of the model are not met.