On the existence and uniqueness of maximum-likelihood estimates in the Rasch model

Necessary and sufficient conditions for the existence and uniqueness of a solution of the so-called unconditional (UML) and the conditional (CML) maximum-likelihood estimation equations in the dichotomous Rasch model are given. The basic critical condition is essentially the same for UML and CML estimation. For complete data matricesA, it is formulated both as a structural property ofA and in terms of the sufficient marginal sums. In case of incomplete data, the condition is equivalent to complete connectedness of a certain directed graph. It is shown how to apply the results in practical uses of the Rasch model.Paper read at the European Meeting of the Psychometric Society, Groningen, June 19–21, 1980.Part of the research reported herein was done while the author was staying at the Pulmologisches Zentrum der Stadt Wien; he is indebted to Professor Dr. F. Muhar and Dr. R. Mutschlechner for providing excellent working conditions.     

Single and multidimensional same-different judgments

A probabilistic, multidimensional Thurstonian model for treating same-different judgments was tested in an experiment in which subjects made single-dimensional and two-dimensional same-different judgments. Strong asymmetries in the data required adding temporal bias parameters to the model. The model, with bias parameters, accounted for the single- and two-dimensional judgments reasonably well, but the parameters were not invariant between the different solutions. The two-dimensional judgments were more variable than expected on the basis of the single-dimensional judgments.     

Eine neue Wahrnehmungstäuschung

Zusammenfassung Die Grenze des durch beide Arme bestimmten menschlichen Doppelgreifraumes hat die Gestalt einer Kugeldoppelhaube. Alle Punkte dieser Grenzfläche sind durch Greifbewegung gleich bequem (noch) erreichbar, wobei der Doppelarm als einheitliches Greif organ aufzufassen ist. Es besteht für diese Fläche nach allen Richtungen Gleichheit der Greifentfernung. Durch Spiegel-Hand-Versuche kann man nunmehr zeigen, daß alle Punkte dieser Grenzfläche bei visueller Wahrnehmung auch vom Auge aus gleichweit entfernt erscheinen, obwohl dies geometrisch schon wegen der exzentrischen Lage des Auges keineswegs der Fall ist. Die Grenze des Doppelgreifraumes nimmt beim Aufbau des menschlichen Sehraumes eine Schlüsselstellung ein.Man kann an dem beschriebenen Phänomen mit Aussicht auf Erfolg neue psychische Grundgesetze aufspüren. Versuche mit sogenannten Contergankindern können hierzu neue Aufschlüsse liefern.

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Summary The periphery delimiting the space circumscribed by the motional range of both human arms takes the shape of a double truncated sphere. All points of this periphery may still be reached with equal ease by a mere gripping motion (regarding, for the purposes of this study, the two arms as a single prehensile organ), and peripheral equidistance of reach exists in all directions. By means of tests in which the outstretched hand is expediently reflected in a mirror it can now be demonstrated that in visual perception (due to the above-mentioned motional equidistance) the entire double-spherical periphery appears equidistant also from the vantage-point of the eye, even though geometrically this is by no means the case. The periphery of the bilateral space of prehension, therefore, assumes a key position in the configuration of space as perceived by the human eye.The phenomenon opens views fowards new basic psychic laws. Also experiments with thalidomide children may provide new insights.

     

Dynamics of oralrespiratory coordination in full-term and preterm infants: I. Comparisons at 38-40 weeks postconceptional age

This study compares the coordination of pacifier sucking and breathing between healthy full-term, low risk preterm, and high risk preterm infants at 38–40 weeks postconceptional age. High and low risk preterm infants did not differ in overall score on a neurobehavioral examination (NAPI), but infants in the high risk group differed from the others in breathing frequency and in the coordination of breathing and sucking rhythms. For infants in the high risk group, sucking had less influence on respiratory frequency and patterns of coordination between the frequencies of sucking and breathing were simpler. Oral–respiratory coordination may be a useful marker of infants at risk for later speech problems.     

Paradoxical consequences of Balzer''s and G?hde''s criteria of theoreticity. Results of an application to ten scientific theories

It is shown that the criteria of T-theoreticity proposed by Balzer and Gähde lead to strongly counterintuitive and in this sense paradoxical results: most of the obviously empirical or at least nontheoretical terms come out as theoretical. This is demonstrated for a lot of theories in different areas. On the way, some improved and some new structuralist theory-reconstructions are given. The conclusion is drawn that the T-theoreticity of a term cannot possibly be proved on the basis of the mathematical structure of theory T alone (as Gähde and Balzer suggest). Rather, an independent notion of pre-T-theoreticity and-more importantly-of empiricity is needed; i.e., not empirical and not pre-T-theoretical are independent, necessary but not sufficient conditions for T-theoretical (this is also a necessary complement of Sneed's original criterion). Finally it is asked whether the structuralist criterion of T-theoreticity complemented by such independent conditions would be a satisfactory answer to Putnam's challenge, and the answer again is negative: the criterion is not able to distinguish between empirically contentful and completely contentless (superfluous) theoretical terms.     

Remarks on “equivalent linear logistic test models” by Bechger,Verstralen, and Verhelst (2002)

This paper discusses a new form of specifying and normalizing a Linear Logistic Test Model (LLTM) as suggested by Bechger, Verstralen, and Verhelst (Psychometrika, 2002). It is shown that there are infinitely many ways to specify the same normalization. Moreover, the relationship between some of their results and equivalent previous results in the literature is clarified, and it is shown that the goals of estimating and testing a single element of the weight matrix, for which they propose new methods, can be reached by means of simple, well-known tools already implemented in published LLTM software.