The authors propose new procedures for evaluating direct, indirect, and total effects in multilevel models when all relevant variables are measured at Level 1 and all effects are random. Formulas are provided for the mean and variance of the indirect and total effects and for the sampling variances of the average indirect and total effects. Simulations show that the estimates are unbiased under most conditions. Confidence intervals based on a normal approximation or a simulated sampling distribution perform well when the random effects are normally distributed but less so when they are nonnormally distributed. These methods are further developed to address hypotheses of moderated mediation in the multilevel context. An example demonstrates the feasibility and usefulness of the proposed methods. Keywords: multilevel model, hierarchical linear model, indirect effect, mediation, moderated mediationIn psychology and other social sciences, hypotheses often concern the causal pathways through which key predictors transmit their effects to specific outcomes. For example, Wei, Mallinckrodt, Russell, and Abraham (2004) examined the extent to which attachment anxiety and avoidance were related to maladaptive perfectionism and, in turn, depressive mood. Similarly, Catanzaro and Laurent (2004) hypothesized that alcohol expectancies play a role in drinking as a means of coping, which then predicts a number of drinking behaviors. In both of these cases, the causal effects of the original predictor are transmitted at least partially through an intervening variable, as diagrammed in Figure 1. In the diagram, the product of the paths labeled a and b represents the indirect effect of X on Y, the path labeled cЈ represents the direct effect of X on Y, and c ϭ ab ϩ cЈ is the total effect of X on Y (Alwin & Hauser, 1975;Bollen, 1987Bollen, , 1989. Depending on the pattern of these effects, the variable M may be called a mediator, a suppressor, or simply an intervening variable (MacKinnon, Krull, & Lockwood, 2000). We generally use the terms mediator and mediation to be consistent with the focus of much of the literature on indirect effects, although our exposition also pertains to other patterns of indirect effects.Within the context of linear regression and path analysis, a number of methods have been proposed for evaluating mediation, and this remains an active area of research (e.g., MacKinnon, Lockwood, Hoffman, West, & Sheets, 2002;MacKinnon, Lockwood, & Williams, 2004;Shrout & Bolger, 2002). Such methods are, however, inappropriate if the analyzed data are actually hierarchical in nature (i.e., composed of two or more nested levels). Two forms of hierarchical data are common in psychological research. First, individuals may be assessed from a number of groups. Individuals are then said to be nested within groups. To the extent that individuals within a group share common experiences, we would expect their scores on the outcome variable to be correlated across members of the group, which violates the independence assumption of ...

No abstract

This study examines pain coping strategies in a relatively neglected pain population, sickle cell disease (SCD) patients. Seventy-nine patients diagnosed with SCD were given a structured interview to assess pain, activity level, and health care use during painful episodes. Patients also completed the SCL-90-R as an index of psychological distress and the Coping Strategies Questionnaire. Regression analyses controlled for age, sex, and disease severity measures. Results indicated that the coping strategies factors were important predictors of pain and adjustment. Individuals high on Negative Thinking and Passive Adherence had more severe pain, were less active and more distressed, and used more health care services. Individuals high on Coping Attempts were more active during painful episodes.

Purpose NRG Oncology/RTOG 1203 was designed to compare patient-reported acute toxicity and health-related quality of life during treatment with standard pelvic radiation or intensity-modulated radiation therapy (IMRT) in women with cervical and endometrial cancer. Methods Patients were randomly assigned to standard four-field radiation therapy (RT) or IMRT radiation treatment. The primary end point was change in patient-reported acute GI toxicity from baseline to the end of RT, measured with the bowel domain of the Expanded Prostate Cancer Index Composite (EPIC). Secondary end points included change in patient-reported urinary toxicity, change in GI toxicity measured with the Patient-Reported Outcome Common Terminology Criteria for Adverse Events, and quality of life measured with the Trial Outcome Index. Results From 2012 to 2015, 289 patients were enrolled, of whom 278 were eligible. Between baseline and end of RT, the mean EPIC bowel score declined 23.6 points in the standard RT group and 18.6 points in the IMRT group ( P = .048), the mean EPIC urinary score declined 10.4 points in the standard RT group and 5.6 points in the IMRT group ( P = .03), and the mean Trial Outcome Index score declined 12.8 points in the standard RT group and 8.8 points in the IMRT group ( P = .06). At the end of RT, 51.9% of women who received standard RT and 33.7% who received IMRT reported frequent or almost constant diarrhea ( P = .01), and more patients who received standard RT were taking antidiarrheal medications four or more times daily (20.4% v 7.8%; P = .04). Conclusion Pelvic IMRT was associated with significantly less GI and urinary toxicity than standard RT from the patient's perspective.

No abstract