Lawrence D. Cohn

How meta-analysis increases statistical power.

One of the most frequently cited reasons for conducting a meta-analysis is the increase in statistical power that it affords a reviewer. This article demonstrates that fixed-effects meta-analysis increases statistical power by reducing the standard error of the weighted average effect size (T.) and, in so doing, shrinks the confidence interval around T.. Small confidence intervals make it more likely for reviewers to detect nonzero population effects, thereby increasing statistical power. Smaller confidence intervals also represent increased precision of the estimated population effect size. Computational examples are provided for 3 effect-size indices: d (standardized mean difference), Pearsons r, and odds ratios. Random-effects meta-analyses also may show increased statistical power and a smaller standard error of the weighted average effect size. However, the authors demonstrate that increasing the number of studies in a random-effects meta-analysis does not always increase statistical power.

Risk-perception: differences between adolescents and adults

This study investigated age changes in risk perception and unrealistic optimism. Teenagers (n = 376) and parents (n = 160) evaluated the risk of experimental, occasional, and regular involvement in 14 health-related activities (e.g., getting drunk). Respondents also evaluated their comparative changes of encountering the leading causes of morbidity and mortality. Compared with adults, teenagers minimized the perceived risk of experimental and occasional involvement in health-threatening activities. Notably, teenagers were less optimistic about avoiding injury and illness than were their parents, and teenagers at greatest risk for such misfortunes were the least optimistic about avoiding them. These findings do not support traditional explanations of adolescent risk taking. The implications of these findings for understanding and preventing health-damaging behavior among adolescents are discussed.

Female and Male Perceptions of Ideal Body Shapes: Distorted Views among Caucasian College Students.

Recent studies have demonstrated that women overestimate male preferences for thin female figures. This study examined whether women also overestimate the desirability of thin figures among female peers. Using body silhouettes employed by Fallon and Rozin (1985), 87 college women and 118 college men indicated the size of their own body figure, their ideal figure, the figure most attractive to other-sex peers, and the figure most attractive to same-sex peers. As predicted, the female silhouette that women selected as most attractive to same-sex peers was significantly thinner than the silhouette that women actually selected as most desirable. College men also misjudged the body preference of same-sex peers, exaggerating the extent to which other men perceived large physiques as ideal and desirable.

Intelligence and maturity: meta-analytic evidence for the incremental and discriminant validity of Loevinger's measure of ego development.

This review examined whether Loevingers measure of personality (ego) development is equivalent to the measurement of intelligence. The authors conducted a meta-analysis of 52 correlations between ego level scores and intelligence test scores (retrieved from 42 studies involving 5,648 participants). The weighted average correlation between ego level and intelligence ranged from.20 to.34, depending on the intellectual ability assessed (e.g., verbal intelligence). Adjusting for measurement unreliability increased these values only minimally. The authors also reviewed 16 studies that examined the association between ego level and various criterion variables (e.g., aggressive behavior) after statistically controlling for the effects of intelligence. Ninety-four percent of the tests revealed significant relations between ego level and criterion variables after controlling for intelligence, indicating that ego development and intelligence are not interchangeable constructs. These findings do not support recent speculations concerning the limited value of stage models of maturity, social development, and moral reasoning.

The validity of self-reported seatbelt use: Hispanic and non-Hispanic drivers in El Paso.

The validity of self-reported seatbelt use among low belt use populations has not been evaluated directly, despite the importance of such data for estimating the effectiveness of community-wide interventions and compliance with state laws. To address this gap in knowledge 612 drivers were recruited from convenience stores located in 12 randomly generated zip code areas located in El Paso, TX. Self-reported seatbelt use was compared with observed seatbelt use in a single sample of participants. Both data sets were collected almost contemporaneously and no participant was aware of having their seatbelt use observed. Hispanic (n = 388) and white/non-Hispanic (n = 126) drivers over reported seatbelt use by 27 and 21%, respectively. These findings suggest that response bias within low belt use populations may be greater than suggested by state and national data.

Adolescent Egocentrism and Feelings of Invulnerability Are they Related

This study examined the relationship between adolescent egocentrism and perceptions of risk in a sample of 458 middle school adolescents. Enrights Adolescent Egocentrism Scale (AES) and Elkinds Imaginary Audience Scale (IAS) were used to assess egocentrism. Analyses revealed unexpected findings regarding the relationship of the two egocentrism scales to risk perception. For females, high scores on the AES were associated with perceptions of high risk, and high scores on the IAS were weakly related to perceptions of low risk. Neither scale was related to risk perceptions for males. Theoretical and measurement issues are discussed.

Adolescent and Adult Mothers' Perceptions of Hazardous Situations for Their Children

PURPOSE To determine if young and inexperienced parents perceive potentially dangerous situations as less hazardous for children than do adult parents. METHODS Sixty expectant adolescent mothers and 45 adult mothers viewed photographs of infants and children in a variety of potentially hazardous situations. Using a 10-point scale, participants estimated the likelihood of injury, the anticipated level of harm, and their own likelihood of intervention in each situation. RESULTS Expectant adolescent mothers were significantly less likely than adult mothers to report intervention in potentially dangerous situations. Previous child care training and experience increased their likelihood of intervention in such hazardous situations. Expectant adolescent mothers perceived greater likelihood of injury for the target child than did adult mothers. CONCLUSIONS Adolescent parents with little child care experience should be alerted to the importance of intervening in potentially hazardous situations for infants and young children.

Seatbelt use and belief in destiny among Hispanic and non-Hispanic drivers

In order to determine if fatalism is associated with seatbelt use, 312 drivers were recruited from convenience stores located within 12 randomly generated zip-code areas along the Texas-Mexico border. The seatbelt use of drivers was recorded unobtrusively; self-reported seatbelt use and belief in destiny (fatalism) were subsequently obtained by interview. The majority of respondents rejected a fatalistic orientation, although Hispanic drivers were significantly less likely to do so. Fatalism was not associated with observed seatbelt use. Our results suggest that ethnic differences in seatbelt use are not due to ethnic differences in fatalism. These findings have implications for developing health interventions in Hispanic and non-Hispanic communities.

A Program to Increase Seat Belt Use Along the Texas–Mexico Border

A school-based, bilingual intervention was developed to increase seat belt use among families living along the Texas-Mexico border. The intervention sought to increase seat belt use by changing perceived norms within the community (i.e., making the nonuse of seat belts less socially acceptable). The intervention was implemented in more than 110 classrooms and involved more than 2100 children. Blind coding, validity checks, and reliability estimates contributed to a rigorous program evaluation. Seat belt use increased by 10% among children riding in the front seat of motor vehicles in the intervention community, as compared with a small but nonsignificant decline in use among control community children. Seat belt use among drivers did not increase.

Perceived Risk of Emerging Recreational Drugs: Impact of Anecdotal and Statistical Evidence:

This study investigated the relative impact of personal stories and base rate evidence on the perceived risk of using two emerging recreational drugs: kratom and Spice. A 3 × 2 × 2 mixed-methods design was employed. Four hundred fifty-three young adults were randomly assigned to read internet postings that presented either 1) base rate information depicting the frequency of adverse reactions to Spice and kratom; 2) base rate information plus four personal web-postings describing beneficial reactions to Spice and kratom; or 3) base rate information plus four personal web-postings describing adverse reactions to Spice and kratom. Respondents subsequently evaluated the risk of using both drugs. Anecdotal evidence (personal stories) outweighed the impact of base rate evidence only when the personal stories described adverse drug reactions. Effective risk communication will benefit from differential use of both base rate evidence and personal stories.