Using segmented linear regression models with unknown change points to analyze strategy shifts in cognitive tasks

Some years ago, Beem (1993, 1995) described a program for fitting two regression lines with an unknown change point (Segcurve). He suggested that such models are useful for the analysis of a variety of phenomena and gave an example of an application to the study of strategy shifts in a mental rotation task. This technique has also proven to be very fruitful for investigating strategy use and strategy shifts in other cognitive tasks. Recently, Beem (1999) developed SegcurvN, which fitsn regression lines with (n - 1) unknown change points. In the present article we present this new technique and demonstrate the usefulness of a three-phase segmented linear regression model for the identification of strategies and strategy shifts in cognitive tasks by applying it to data from a numerosity judgment experiment. The advantages and shortcomings of this technique are evaluated.     

A program for fitting two-phase segmented-curve models with an unknown change point,with an application to the analysis of strategy shifts in a cognitive task

A program is described for fitting a regression model in which the relationship between the dependent and the independent variables is described by two regression equations, one for each of two mutually exclusive ranges of the independent variable. The point at which the change from one equation to the other occurs is often unknown, and thus must be estimated. In cognitive psychology, such models are relevant for studying the phenomenon of strategy shifts. The program uses a (weighted) least squares algorithm to estimate the regression parameters and the change point. The algorithm always finds the global minimum of the error sum of squares. The model is applied to data from a mental-rotation experiment. The program’s estimates of the point at which the strategy shift occurs are compared with estimates obtained from a nonlinear least squares minimization procedure in SPSSX.     

Psychological functioning of recently bereaved, middle-aged women: the first 13 months

This study examined the natural course of psychological functioning in recently bereaved middle-aged women. 69 widows were assessed four times (T1-T4) between the period of 4 to 13 mo. after the loss and were compared to a matched nonwidowed group of 57. Of the SCL-90 feelings of depression, agoraphobic behavior, anxiety, hostility, somatization, feelings of insufficiency, and sleep disorders were heightened at 4 mo. after bereavement compared to the norm group. Significantly higher psychological dysfunctioning was found on all SCL-90 subscales than for non-widows. Over time, a decrease in psychological dysfunction was found for most widows; however, not every widow appeared to recover psychologically, and 17% of the widows showed severe psychological dysfunctioning at 13 mo. postbereavement (T4). With respect to the predictive value of the Total score on the SCL-90, at 13 mo., 27% of these widows had scores indicating severe psychological dysfunctioning; these were comparable to their scores at 4 mo. postbereavement.