Yvonnick Noël

A Beta Item Response Model for Continuous Bounded Responses.

An item response model is proposed for the analysis of continuous response formats in an item response theory (IRT) framework. With such formats, respondents are asked to report their response as a mark on a fixed-length graphical segment whose ends are labeled with extreme responses. An interpolation process is proposed as the response mechanism in this situation, from which the authors show that a beta distribution on the response naturally follows. The two natural parameters of the beta are expressed as monotonic functions of person and item distance on some latent continuum. It is shown that a logistic expected response function results from a simple choice for these monotonic functions. A joint maximum likelihood estimation procedure is presented that performs well in a simulation study. An application on mood items is also presented, with very good fit properties.

An ordination approach to the quantification of smokers' readiness to change

The paper argues that the problem of estimating a “readiness-to-change” score for smokers from processes of change measures is closely related to dating problems in archaeology. It amounts to finding a joint ordination of both smokers (“sites”) and processes of change (“tools”) in a common space, so that smokers be located close to processes they use most, in some sense. Properties of Correspondence Analysis as a reciprocal averaging technique are first briefly summarized, and its capability of recovering nonlinear structures is recalled. Application to processes of change data in smoking cessation leads to a solution which first axis is interpreted as a cognitive-behavioral continuum. Processes are shown to be scaled in a way that is in good convergence with longitudinal data previously reported (Prochaska et al., 1991), and subjects’ locations to be significantly related to actual quitting. Finally, it is shown how new responses profiles could be projected on the obtained solution to get a practical estimation of probability to quit.