Power to Detect What? Considerations for Planning and Evaluating Sample Size.

ACADEMIC ABSTRACT: In the wake of the replication crisis, social and personality psychologists have increased attention to power analysis and the adequacy of sample sizes. In this article, we analyze current controversies in this area, including choosing effect sizes, why and whether power analyses should be conducted on already-collected data, how to mitigate the negative effects of sample size criteria on specific kinds of research, and which power criterion to use. For novel research questions, we advocate that researchers base sample sizes on effects that are likely to be cost-effective for other people to implement (in applied settings) or to study (in basic research settings), given the limitations of interest-based minimums or field-wide effect sizes. We discuss two alternatives to power analysis, precision analysis and sequential analysis, and end with recommendations for improving the practices of researchers, reviewers, and journal editors in social-personality psychology. PUBLIC ABSTRACT: Recently, social-personality psychology has been criticized for basing some of its conclusions on studies with low numbers of participants. As a result, power analysis, a mathematical way to ensure that a study has enough participants to reliably "detect" a given size of psychological effect, has become popular. This article describes power analysis and discusses some controversies about it, including how researchers should derive assumptions about effect size, and how the requirements of power analysis can be applied without harming research on hard-to-reach and marginalized communities. For novel research questions, we advocate that researchers base sample sizes on effects that are likely to be cost-effective for other people to implement (in applied settings) or to study (in basic research settings). We discuss two alternatives to power analysis, precision analysis and sequential analysis, and end with recommendations for improving the practices of researchers, reviewers, and journal editors in social-personality psychology.

Postprandial Plasma Glucose between 4 and 7.9 h May Be a Potential Diagnostic Marker for Diabetes.

Postprandial glucose levels between 4 and 7.9 h (PPG4-7.9h) correlate with mortality from various diseases, including hypertension, diabetes, cardiovascular disease, and cancer. This study aimed to assess if predicted PPG4-7.9h could diagnose diabetes. Two groups of participants were involved: Group 1 (4420 participants) had actual PPG4-7.9h, while Group 2 (8422 participants) lacked this measure but had all the diabetes diagnostic measures. Group 1 underwent multiple linear regression to predict PPG4-7.9h using 30 predictors, achieving accuracy within 11.1 mg/dL in 80% of the participants. Group 2 had PPG4-7.9h predicted using this model. A receiver operating characteristic curve analysis showed that predicted PPG4-7.9h could diagnose diabetes with an accuracy of 87.3% in Group 2, with a sensitivity of 75.1% and specificity of 84.1% at the optimal cutoff of 102.5 mg/dL. A simulation on 10,000 random samples from Group 2 revealed that 175 participants may be needed to investigate PPG4-7.9h as a diabetes diagnostic marker with a power of at least 80%. In conclusion, predicted PPG4-7.9h appears to be a promising diagnostic indicator for diabetes. Future studies seeking to ascertain its definitive diagnostic value might require a minimum sample size of 175 participants.

Contact-implicit preference relationships: Two large sample tests.

This work examines relationships between friendships and implicit preferences across two large samples. There is considerable evidence in the contact literature suggesting that friendships relate to more favorable attitudes toward outgroups, however, most evidence reflects explicit self-report measures. Using samples of 235,543 participants who completed the Disability IAT and 533,220 participants who completed the Sexuality IAT on the Project Implicit website, results indicate that participants reporting either a disabled friend or close acquaintance demonstrated weaker implicit preferences for abled over disabled people. Similarly, those with gay friends demonstrated weaker implicit preference for "straight" over gay. The size of these relationships were considerably smaller than found for explicit evaluations. These effect size estimates should be useful to researchers studying contact-implicit preference relationships as it informs power analyses and sample size planning decisions.

Does women's anxious jealousy track changes in steroid hormone levels?

Findings for progesterone and anxiety in non-human animals led to the hypothesis that women's interpersonal anxiety will track changes in progesterone during the menstrual cycle. There have been few direct tests of this hypothesis, however. Consequently, we used a longitudinal design to investigate whether interpersonal anxiety (assessed using the anxious jealousy subscale of the relationship jealousy questionnaire) tracked changes in salivary steroid hormones during the menstrual cycle in a large sample of young adult women. We found no evidence for within-subject effects of progesterone, estradiol, their interaction or ratio, testosterone, or cortisol on anxious jealousy. There was some evidence that other components of jealousy (e.g., reactive jealousy) tracked changes in women's cortisol, however. Collectively, these results provide no evidence for the hypothesis that interpersonal anxiety tracks changes in progesterone during the menstrual cycle.

Diversity experiences predict changes in attitudes toward affirmative action.

The current study examined the role of diversity experiences in promoting changes in attitudes toward affirmative action (AA). Using longitudinal data from a survey of over 1000 college students at admission and in their fourth year, results demonstrated that participation in diversity-related campus activities related to positive changes in attitudes toward affirmative action. This result was consistent across samples of White, African American, and Asian American students. Positive changes in attitudes persisted despite statistical controls for established predictors of attitudes toward AA such as merit and prevalence of discrimination beliefs, and individual-level characteristics such as experiences of discrimination and political liberalism. I discuss the relevance of this finding to the AA literature and to changing attitudes toward AA.

Does substance use affect reliabilities of the Implicit Association Test?

The authors examined whether use of alcohol or marijuana affected reliability of the Implicit Association Test (IAT; A. G. Greenwald, D. E. McGhee, & J. L. K. Schwartz, 1998). Consistent with research indicating the possibility that marijuana use depletes cognitive resources, the authors found worse reliabilities for participants who recently used marijuana than for those who had not. Recent alcohol users and nonusers demonstrated similar IAT reliability. Subsequent analyses indicated that reliability differences between marijuana users and nonusers were most pronounced when participants began with incongruous tasks and then switched to congruous tasks. Results were consistent with work on the residual costs of task switching that indicates that effortful tasks promote interference with tasks that follow. The authors discussed results in terms of IAT scoring procedures and the prevalence of use of alcohol and marijuana on university campuses.

Implicit bias and contact: the role of interethnic friendships.

In 2 studies, the authors examined the role of interethnic friendship with African Americans or Latinos in predicting implicit and explicit biases against these groups. White participants completed the Implicit Association Test (IAT; Greenwald, A. G., McGhee, D. E., & Schwartz, J. L. K., 1998), several self-report bias measures, and a friendship questionnaire. Participants with close friends who were members of the target group exhibited less implicit prejudice than participants without close friends from the target group. Friendship influenced only 2 of the 7 explicit measures, a result that likely stems from social desirability bias rather than truly non-prejudiced attitudes. Results support the importance of contact, particularly interethnic friendship, in improving intergroup attitudes.

The damage done: a study of injection drug use, injection related abscesses and needle exchange regulation.

This study investigated the impact of a needle exchange policy change on community health. Data were collected from a needle exchange program in Eureka, California, for clients who participated in the program between the weeks (n = 112) of January 1, 2002, and February 28, 2004. Analysis was done using an autoregressive integrated moving average (ARIMA), indicating that greater utilization of the needle exchange program, in terms of needles exchanged and number of visits, is related to fewer numbers of abscesses treated. Additionally, self-report data collected from former intravenous drug users (n = 62) demonstrated that more needles exchanged were related to fewer occurrences of abscesses. The limitations of this research are discussed.