Statistical Methodology for the Analysis of Repeated Duration Data in Behavioral Studies.

Purpose: Repeated duration data are frequently used in behavioral studies. Classical linear or log-linear mixed models are often inadequate to analyze such data, because they usually consist of nonnegative and skew-distributed variables. Therefore, we recommend use of a statistical methodology specific to duration data. Method: We propose a methodology based on Cox mixed models and written under the R language. This semiparametric model is indeed flexible enough to fit duration data. To compare log-linear and Cox mixed models in terms of goodness-of-fit on real data sets, we also provide a procedure based on simulations and quantile-quantile plots. Results: We present two examples from a data set of speech and gesture interactions, which illustrate the limitations of linear and log-linear mixed models, as compared to Cox models. The linear models are not validated on our data, whereas Cox models are. Moreover, in the second example, the Cox model exhibits a significant effect that the linear model does not. Conclusions: We provide methods to select the best-fitting models for repeated duration data and to compare statistical methodologies. In this study, we show that Cox models are best suited to the analysis of our data set.

Force sharing and neutral line during finger extension tasks.

There is general consensus that the minimization of the secondary torque of the hand provides a universal model for explaining the force sharing patterns among the fingers. Since biomechanical secondary axes of the hand are unchanged in extension, it appears relevant to validate this model for finger extension forces. Fifteen subjects performed flexion and extension forces in a four-finger task. Each fingertip force was expressed in percentage of the force produced by an individual finger force over the resultant four-finger force (force sharing), and the point of force application of the resultant force was calculated (neutral line). The force-sharing pattern was different for flexion and extension. The index and ring fingers were equally involved, regardless of the task. The neutral line was located differently in flexion and extension, and for proximal and distal force application in extension. The mode of control of the finger redundancy was specific to the force production in flexion and extension. In flexion, the principle of minimization of secondary torque was confirmed. This was not observed in extension. We concluded that the minimization of the secondary torque is not a universal mode of control of the finger redundancy.