Summary Results obtained in randomized trials may not easily generalize to target populations. Whereas in randomized trials the treatment assignment mechanism is known, the sampling mechanism by which individuals are selected to participate in the trial is typically not known and assuming random sampling from the target population is often dubious. We consider an inverse probability of sampling weighted (IPSW) estimator for generalizing trial results to a target population. The IPSW estimator is shown to be consistent and asymptotically normal. A consistent sandwich-type variance estimator is derived and simulation results are presented comparing the IPSW estimator to a previously proposed stratified estimator. The methods are then utilized to generalize results from two randomized trials of HIV treatment to all people living with HIV in the United States.
Great care is taken in epidemiologic studies to ensure the internal validity of causal effect estimates; however, external validity has received considerably less attention. When the study sample is not a random sample of the target population, the sample average treatment effect, even if internally valid, cannot usually be expected to equal the average treatment effect in the target population. The utility of an effect estimate for planning purposes and decision making will depend on the degree of departure from the true causal effect in the target population due to problems with both internal and external validity. Herein, we review concepts from recent literature on generalizability, one facet of external validity, using the potential outcomes framework. Identification conditions sufficient for external validity closely parallel identification conditions for internal validity, namely: conditional exchangeability; positivity; the same distributions of the versions of treatment; no interference; and no measurement error. We also require correct model specification. Under these conditions, we discuss how a version of direct standardization (the g-formula, adjustment formula, or transport formula) or inverse probability weighting can be used to generalize a causal effect from a study sample to a well-defined target population, and demonstrate their application in an illustrative example.
Objective. To evaluate the impact of a six-week yoga and meditation intervention on college students' stress perception, anxiety levels, and mindfulness skills. Methods. College students participated in a six-week pilot program that consisted of a 60-minute vinyasa flow yoga class once weekly, followed by guided meditation delivered by trained faculty members at the University of Rhode Island College of Pharmacy. Students completed pre-and postintervention questionnaires to evaluate changes in the following outcomes: stress levels, anxiety levels, and mindfulness skills. The questionnaire consisted of three self-reporting tools: the Beck Anxiety Inventory (BAI), the Perceived Stress Scale (PSS), and the Five Facet Mindfulness Questionnaire (FFMQ). Students' scores on each were assessed to detect any changes from baseline using the numerical and categorical scales (low, medium, and high) for each instrument. Results. Seventeen participants, aged 19 to 23 years, completed the study. Thirteen participants were female and four were male. Nine of the students were enrolled in the Doctor of Pharmacy program and eight were enrolled in other academic programs. Students' anxiety and stress scores decreased significantly while their total mindfulness increased significantly. Changes in categorical data from pre-to post-intervention on the BAI and PSS were significant, with no students scoring in the "high" category for stress or anxiety on the post-intervention questionnaire. Conclusion. Students experienced a reduction in stress and anxiety levels after completing a six-week yoga and meditation program preceding final examinations. Results suggest that adopting a mindfulness practice for as little as once per week may reduce stress and anxiety in college students. Administrators should consider including instruction in nonpharmacologic stress and anxiety reduction methods, within curricula in order to support student self-care.
Lack of agreement was observed for more than half of the studied barriers, indicating discrepancies between children's and caregivers' perceptions of factors that influence medication-taking. The findings suggest a need for interventions that involve both child and caregiver in the tasks of remembering when to administer the child's medications, sustaining adherence, and appropriately transitioning medication responsibility to the youth.
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