Browsing by Author "Samejima, Fumiko"

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    Effects of individual optimization in setting the boundaries of dichotomous items on accuracy of estimation
    (1977) Samejima, Fumiko
    Applying the normal ogive model of latent trait theory, two sets of data, simulated and empirical, were analyzed. The objective was to determine how much accuracy of estimation of the subjects’ latent ability can be maintained by tailoring for each testee the order of presentation of the items and the border of dichotomization for each item. This was compared to the information provided by the original graded test items. Results indicated that tailored testing is promising especially when the number of items is not too small, and that a graded item can effectively be used as the initial item in tailored testing because of its branching effect.
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    Estimation of reliability coefficients using the test information function and its modifications
    (1994) Samejima, Fumiko
    The reliability coefficient and the standard error of measurement in classical test theory are not properties of a specific test, but are attributed to both a specific test and a specific trait distribution. In latent trait models, or item response theory, the test information function (TIF) provides more precise local measures of accuracy in trait estimation than are available from the reliability coefficient. The reliability coefficient is still widely used, however, and is popular because of its simplicity. Thus, it is worthwhile to relate it to the TIF. In this paper, the reliability coefficient is predicted from the TIF, or two modified TIF formulas, and a specific trait distribution. Examples demonstrate the variability of the reliability coefficient across different trait distributions, and the results are compared with empirical reliability coefficients. Practical suggestions are given as to how to make better use of the reliability coefficient. Index terms: adaptive testing, bias, classical test theory, item information function, latent trait models, maximum likelihood estimation, reliability coefficient, standard error of measurement, test information function, trait estimation.
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    Nonparametric estimation of the plausibility functions of the distractors of vocabulary test items
    (1994) Samejima, Fumiko
    The Level II Vocabulary Subtest of the Iowa Tests of Basic Skills was analyzed using a two-stage latent trait approach and an empirical dataset of 2,356 examinees. First, each of the 43 multiplechoice test items was scored dichotomously; then, assuming the (two-parameter) normal ogive model the item parameters were estimated. The operating characteristics of the correct answer and of the three distractors were estimated using a nonparametric approach called the simple sum procedure of the conditional probability density function approach combined with the normal approach method. Differential information was provided by the distractors, and these operating characteristics were named the plausibility functions of the distractors. The operating characteristic of the correct answer of each item estimated by assuming the normal ogive model was compared with the nonparagnetrically estimated operating characteristic for model validation. It was concluded that the nonparametric approach leads to efficient estimation of the latent trait. Index terms: distractors, item response theory, latent trait models, multiple-choice test items, nonparametric estimation, plausibility functions of distractors.
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    A use of the information function in tailored testing
    (1977) Samejima, Fumiko
    Several important and useful implications in latent trait theory, with direct implications for individualized adaptive or tailored testing, are pointed out. A way of using the information function in tailored testing in connection with the standard error of estimation of the ability level using maximum likelihood estimation is suggested. It is emphasized that the standard error of estimation should be considered as the major index of dependability, as opposed to the reliability of a test. The concept of weak parallel forms is expanded to testing procedures in which different sets of items are presented to different examinees. Examples are given. Researchers have tended to use latent trait theory rather than classical test theory in research on individualized adaptive or tailored testing. This is quite natural, since latent trait theory has definite merits over classical test theory in many crucial matters. Because of the lack of opportunities to really learn the theory, however, these researchers tend to overlook some important implications in latent trait theory. As a result, its full use has not yet materialized. Not only are information functions seldom used to maximum advantage, but also those who have tried to use latent trait theory still use some popular concepts in classical test theory, such as reliability. expanded to testing procedures in which different sets of items are presented to different examinees. Examples are given. In this paper, the author points out some important implications in latent trait theory which are not fully understood and appreciated among researchers, and gives some practical suggestions for its use.