This software review discusses the capabilities of Stata to conduct item response theory modeling. The commands needed for fitting the popular one-, two-, and three-parameter logistic models are initially discussed. The procedure for testing the discrimination parameter equality in the one-parameter model is then outlined. The commands for fitting…

Mixture Rasch (MixRasch) models conventionally assume normal distributions for latent ability. Previous research has shown that the assumption of normality is often unmet in educational and psychological measurement. When normality is assumed, asymmetry in the actual latent ability distribution has been shown to result in extraction of spurious…

The answer to the question, "Ability, speed, or both?" may be "both at once" if speed is simply a manifestation of ability. If differences in speed are manifestations of differences in ability, then both speed and ability may reflect a single dimension best characterized by a single score. While measurement of speed has proven…

Merrill Hiscock presents two criticisms of Clark's analysis of the Flynn effect. The first is that the authors worry too much about general ability and pay too little attention to multifactorial concepts of intelligence. The second applies not only to the Clark et al. paper but to the Flynn effect literature in general--namely, neglect of the…

It is commonly acknowledged that ability and speed are not separate constructs but interact with each other. Traditionally, the ability-speed interplay has been seen as a problem to be conquered and a number of psychometric methods have been developed to deal with the interplay between ability and speed and to obtain more pure ability measures.…

In this commentary, Kuhn and Ranger hypothesize that most people are aware that talent does not guarantee success in case one is lazy. This is also true for the performance in achievement tests that depends on, among other factors, achievement potential (ability) and willingness to achieve (test-taking motivation) of the test taker. They add that…

A new and very interesting approach to the analysis of responses and response times is proposed by Goldhammer (this issue). In his approach, differences in the speed-ability compromise within respondents are considered to confound the differences in ability between respondents. These confounding effects of speed on the inferences about ability can…

Goldhammer (this issue) proposes an interesting approach to dealing with the speededness of item responses. Rather than modeling speed as a latent variable that varies from person to person, he proposes to use experimental conditions that are expected to fix the speed, thereby eliminating individual differences on this dimension in order to make…

The excellent paper by Goldhammer (this issue) deals with a most relevant and very pervasive problem of ability assessment: the evaluation of performance by considering speed and accuracy of performance. Goldhammer proposes item-level time limits as a possible remedy for individual differences in the speed-accuracy trade-off (SATO) to keep time…

The main challenge of ability tests relates to the difficulty of items, whereas speed tests demand that test takers complete very easy items quickly. This article proposes a conceptual framework to represent how performance depends on both between-person differences in speed and ability and the speed-ability compromise within persons. Related…

This paper addresses two problems relating to the interpretability of the model parameters in the three parameter logistic model. First, it is shown that if the values of the discrimination parameters are all the same, the remaining parameters are nonidentifiable in a nontrivial way that involves not only ability and item difficulty, but also the…

"The Second Century of Ability Testing: Some Predictions and Speculations" did not include predictions about the ability construct or the role of fundamental measurement principles. All commentators raised issues about the nature of the ability construct. The diverse viewpoints represented in these comments highlight well the complexity…

The last century was marked by dazzling changes in many areas, such as technology and communications. Predictions into the second century of testing are seemingly difficult in such a context. Yet, looking back to the turn of the last century, Kirkpatrick (1900), in his American Psychological Association presidential address, presented fundamental…