The effects of intercessory prayer, positive visualization, and expectancy on the well-being of kidney dialysis patients.

CONTEXT: Little replicable empirical evidence on the effectiveness of prayer is available. OBJECTIVE: To explore the effect of intercessory prayer, positive visualization, and outcome expectancy on a wide range of medical and psychological measures in critically ill patients. DESIGN: 2 x 3 (expectancy x treatment) factorial study. PARTICIPANTS: 95 adult male and female volunteer hemodialysis subjects with end-stage renal disease from an outpatient clinic in Miami, Fla. INTERVENTION: Participants were randomly assigned to 1 of the 6 treatment conditions. MAIN OUTCOME MEASURES: A total of 20 dependent measures (10 medically based and 10 psychological) were used to assess the subjects' overall well-being. Analysis of covariance was used to control for pre-treatment differences between groups. RESULTS: Subjects who expected to receive intercessory prayer reported feeling significantly better than did those who expected to receive positive visualization (F1.93 = 5.42; P < .02). No other statistically significant main effects or interactions were found for either expectancy, intercessory prayer, or positive visualization on the remaining dependent measures. Analysis of effect sizes on all dependent measures failed to indicate even a small magnitude of effect for intercessory prayer as contrasted with expectancy on the medical or psychological variables. CONCLUSIONS: The effects of intercessory prayer and transpersonal positive visualization cannot be distinguished from the effect of expectancy. Therefore, those 2 interventions do not appear to be effective treatments.

Using Multidimensional Scaling to Assess the Dimensionality of Dichotomous Item Data.

In this study, we investigated the utility of multidimensional scaling (MDS) for assessing the dimensionality of dichotomous test data. Two MDS proximity measures were studied: one based on the PC statistic proposed by Chen and Davison (1996), the other based on inter-item Euclidean distances. Stout's (1987) test of essential unidimensionality (DIMTEST) was also used as a standard for comparison. Twenty different conditions of unidimensional and multidimensional data were simulated, varying the number of test items, correlations among dimensions, and type of data generation model (Rasch or two-parameter IRT model). DIMTEST performed best overall, but had some trouble detecting multidimensionality when the number of test items was small. The PC statistic correctly identified the dimensionality of the unidimensional data, whereas the use of Euclidean distances suggested the two-parameter unidimensional data were multidimensional. Both MDS procedures correctly identified multidimensionality under the low correlation conditions, but were generally unable to detect multidimensionality when the dimensions were highly correlated. Analysis of Euclidean distances were best for determining the precise dimensionality of the multidimensional data under the low correlation condition. Implications of the findings are discussed, and suggestions for future research are provided.

Evaluating the predictive validity of MCAT scores across diverse applicant groups.

PURPOSE: To examine the predictive validity of MCAT scores, alone and in combination with other preadmission data, for medical students grouped by race/ethnicity and sex. METHOD: This study included two samples: 1,109 students who entered in 1992 any of the 14 medical schools participating in the MCAT Predictive Validity Study; and all 11,279 students who entered medical school in 1992 and took the USMLE Step 1 in June 1994. Criterion measures included each student's cumulative GPA in the first two years of medical school and his or her pass/fail status on Step 1. Differential predictive validity was examined by comparing prediction errors across racial/ethnic and sex groups. For cumulative GPA; residuals were compared, and for Step 1, classification errors were studied. RESULTS: The patterns of prediction errors observed across the groups indicated that, on average, (1) no difference between the sexes in prediction errors was evident; (2) performances of the three racial/ethnic minority groups tended to be overpredicted, with significant findings for Asians and Hispanics; and (3) Caucasians' performance tended to be underpredicted, although the magnitude of this underprediction was quite small. When USMLE Step 1 scores were the criterion for success in medical school, the majority of errors were overprediction errors. CONCLUSION: The authors caution that although MCAT scores, alone and in combination with undergraduate GPA, are good predictors of medical school performance, they are not perfect. The authors encourage future research exploring additional predictor variables, such as diligence, motivation, communication skills, study habits, and other relevant characteristics. Similarly, they indicate that high grades and Step 1 scores are not the only indicators of success in the medical profession and call for studies examining other important qualities, such as integrity, interpersonal skills, capacity for caring, willingness to commit to lifelong learning, and desire to serve in underserved areas.