Exact distributions of intraclass correlation and Cronbach's alpha with Gaussian data and general covariance

Intraclass correlation and Cronbach's alpha are widely used to describe reliability of tests and measurements. Even with Gaussian data, exact distributions are known only for compound symmetric covariance (equal variances and equal correlations). Recently, large sample Gaussian approximations were derived for the distribution functions. New exact results allow calculating the exact distribution function and other properties of intraclass correlation and Cronbach's alpha, for Gaussian data with any covariance pattern, not just compound symmetry. Probabilities are computed in terms of the distribution function of a weighted sum of independent chi-square random variables. NewF approximations for the distribution functions of intraclass correlation and Cronbach's alpha are much simpler and faster to compute than the exact forms. Assuming the covariance matrix is known, the approximations typically provide sufficient accuracy, even with as few as ten observations. Either the exact or approximate distributions may be used to create confidence intervals around an estimate of reliability. Monte Carlo simulations led to a number of conclusions. Correctly assuming that the covariance matrix is compound symmetric leads to accurate confidence intervals, as was expected from previously known results. However, assuming and estimating a general covariance matrix produces somewhat optimistically narrow confidence intervals with 10 observations. Increasing sample size to 100 gives essentially unbiased coverage. Incorrectly assuming compound symmetry leads to pessimistically large confidence intervals, with pessimism increasing with sample size. In contrast, incorrectly assuming general covariance introduces only a modest optimistic bias in small samples. Hence the new methods seem preferable for creating confidence intervals, except when compound symmetry definitely holds. An earlier version of this paper was submitted in partial fulfillment of the requirements for the M.S. in Biostatistics, and also summarized in a presentation at the meetings of the Eastern North American Region of the International Biometric Society in March, 2001. Kistner's work was supported in part by NIEHS training grant ES07018-24 and NCI program project grant P01 CA47 982-04. She gratefully acknowledges the inspiration of A. Calandra's “Scoring formulas and probability considerations” (Psychometrika, 6, 1–9). Muller's work supported in part by NCI program project grant P01 CA47 982-04.     

Inner speech sustains predictable task switching: direct evidence in adults

It has been proposed that inner speech supports task selection in task-switching studies, especially when the need for endogenous control is increased. This has been established through the suppression of inner speech in cognitive-flexibility tasks that leads to poorer performance. The aim of this study is to quantify the role of inner speech in a flexibility task by using surface laryngeal electromyography, which, contrary to previous studies, enables participants to freely verbalise the tasks. We manipulated endogenous and exogenous flexibility in a mathematical switching task paradigm. Experiment 1 shows that inner speech acts as a support for switching and is recruited more often when the tasks are of an endogenous type. The main result of Experiment 2 that language is recruited more for the mixing cost than for the switch cost (regardless of the endogenous factor) extends past findings obtained through articulatory suppression.     

Joint factor analysis of the Children's Depression Inventory and the Revised Children's Manifest Anxiety Scale.

Used a joint factor analysis with the Children's Depression Inventory (CDI; Kovacs, 1980/81, 1992) and Revised Children's Manifest Anxiety Scale (RCMAS; C. R. Reynolds & Richmond, 1978, 1985) to identify items that uniquely measured depression and anxiety. Data from 750 youngsters in Grades 4 through 7 were analyzed using principal-axis factoring with an oblique rotation. Salient factors were identified using guidelines provide by Gorsuch (1997). Item overlap and the large negative affectivity component across instruments were evident. Items that overlapped or had nonsalient loadings were eliminated. The sample was randomly split into 2 groups of 375 and analyses were repeated. Results indicated that a unique 9-item depression factor composed largely of items representing a negative view of oneself existed. In addition, a unique 7-item anxiety factor emerged that consisted of items reflecting worry. The validity of these abbreviated scales was explored using a separate sample of 131 students in Grades 4 through 9. The abbreviated scales were correlated with scales of positive and negative affect consistent with predictions. Findings suggest exploring alternative scoring strategies for the CDI and RCMAS to eliminate problems associated with overlapping items.     

Supervisor Trustworthiness and Subordinates' Willingness to Provide Extra‐Role Efforts1

A laboratory experiment was used to determine the separate and joint effects of behaviors denoting supervisor trustworthiness on subordinate willingness to provide the supervisor with extra‐role efforts. Results indicate that a supervisor's demonstration of benevolence toward the subordinate outweighed the supervisor's work‐relevant ability and his or her benevolence toward the subordinate's peers in positively influencing subordinate willingness to provide the supervisor with extra‐role efforts. Also, benevolence toward the subordinate's peers moderated the effect of benevolence toward the subordinate, whereby benevolence toward the subordinate had a reduced positive effect when the supervisor was not benevolent toward the subordinate's peers.     

The influence of threat and aversive motivation on conflict processing in the Stroop task

Attention, Perception, & Psychophysics - Motivated attention can be driven by the desire to maximize gains or escape punishment. In the Stroop task, when rewards can be obtained by responding...     

The study of locomotor pointing in virtual reality: The validation of a test set-up

The goal of this experiment was to validate an experimental set-up for studying locomotor pointing. The specific and also original element of this set-up was the interactive nature of virtual reality and movement production. This interaction was achieved through the coupling of a treadmill and a Silicon Graphics system. This latter system generated on a screen (3 × 2.3 m) an environmental array that moved according to the action produced by subjects on a treadmill. The task was to place either foot on a spatial target that appeared on the floor in front of the subject’s displacement trajectory. We analyzed the step length patterns of subjects approaching these targets, along with the current target-subject relationship. The results are in agreement with aperception-action coupling type of control mechanism that operates continuously as the subject approaches the desired target. Apparently, these findings mirror observations of real-life locomotion, indicating that the present set-up provides a valid and useful tool for examining human locomotion.     

Too fatigued to care: Ego depletion,guilt, and prosocial behavior

Although guilt feels bad to the individual, it is good for society because guilty feelings can prompt people to perform good deeds. This study tests whether fatigue decreases guilty feelings and subsequent prosocial behavior. Participants were randomly assigned to a depletion condition in which they watched a movie about butchering animals for their meat or skin and were told to express no emotions, or to a no-depletion condition in which they watched the same movie, but could express their emotions. Having participants play a game in which another person was punished for their errors induced guilt. Finally, participants played a dictator game in which they could leave money for the next participant. After the experiment, participants could also anonymously donate money to an anti-AIDS charity. The results showed that depleted participants felt less guilty than did non-depleted participants, and the less guilty participants felt the less helpful they were.