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Concept: Gene V. Glass


There is increasing evidence that gardening provides substantial human health benefits. However, no formal statistical assessment has been conducted to test this assertion. Here, we present the results of a meta-analysis of research examining the effects of gardening, including horticultural therapy, on health. We performed a literature search to collect studies that compared health outcomes in control (before participating in gardening or non-gardeners) and treatment groups (after participating in gardening or gardeners) in January 2016. The mean difference in health outcomes between the two groups was calculated for each study, and then the weighted effect size determined both across all and sets of subgroup studies. Twenty-two case studies (published after 2001) were included in the meta-analysis, which comprised 76 comparisons between control and treatment groups. Most studies came from the United States, followed by Europe, Asia, and the Middle East. Studies reported a wide range of health outcomes, such as reductions in depression, anxiety, and body mass index, as well as increases in life satisfaction, quality of life, and sense of community. Meta-analytic estimates showed a significant positive effect of gardening on the health outcomes both for all and sets of subgroup studies, whilst effect sizes differed among eight subgroups. Although Egger’s test indicated the presence of publication bias, significant positive effects of gardening remained after adjusting for this using trim and fill analysis. This study has provided robust evidence for the positive effects of gardening on health. A regular dose of gardening can improve public health.

Concepts: Health care, Epidemiology, Statistical significance, Middle East, Effect size, Meta-analysis, Statistical power, Gene V. Glass


OBJECTIVE: Walking groups are increasingly being set up but little is known about their efficacy in promoting physical activity. The present study aims to assess the efficacy of interventions to promote walking in groups to promoting physical activity within adults, and to explore potential moderators of this efficacy. METHOD: Systematic literature review searches were conducted using multiple databases. A random effect model was used for the meta-analysis, with sensitivity analysis. RESULTS: The effect of the interventions (19 studies, 4 572 participants) on physical activity was of medium size (d = 0.52), statistically significant (95%CI 0.32 to 0.71, p < 0.0001), and with large fail-safe of N = 753. Moderator analyses showed that lower quality studies had larger effect sizes than higher quality studies, studies reporting outcomes over six months had larger effect sizes than studies reporting outcomes up to six months, studies that targeted both genders had higher effect sizes than studies that targeted only women, studies that targeted older adults had larger effect sizes than studies that targeted younger adults. No significant differences were found between studies delivered by professionals and those delivered by lay people. CONCLUSION: Interventions to promote walking in groups are efficacious at increasing physical activity. Despite low homogeneity of results, and limitations (e.g. small number of studies using objective measures of physical activity, publication bias), which might have influence the findings, the large fail-safe N suggests these findings are robust. Possible explanations for heterogeneity between studies are discussed, and the need for more investigation of this is highlighted.

Concepts: Systematic review, Statistical significance, Effectiveness, Efficacy, Effect size, Meta-analysis, Statistical power, Gene V. Glass


Gene expression data, in conjunction with information on genetic variants, have enabled studies to identify expression quantitative trait loci (eQTLs) or polymorphic locations in the genome that are associated with expression levels. Moreover, recent technological developments and cost decreases have further enabled studies to collect expression data in multiple tissues. One advantage of multiple tissue datasets is that studies can combine results from different tissues to identify eQTLs more accurately than examining each tissue separately. The idea of aggregating results of multiple tissues is closely related to the idea of meta-analysis which aggregates results of multiple genome-wide association studies to improve the power to detect associations. In principle, meta-analysis methods can be used to combine results from multiple tissues. However, eQTLs may have effects in only a single tissue, in all tissues, or in a subset of tissues with possibly different effect sizes. This heterogeneity in terms of effects across multiple tissues presents a key challenge to detect eQTLs. In this paper, we develop a framework that leverages two popular meta-analysis methods that address effect size heterogeneity to detect eQTLs across multiple tissues. We show by using simulations and multiple tissue data from mouse that our approach detects many eQTLs undetected by traditional eQTL methods. Additionally, our method provides an interpretation framework that accurately predicts whether an eQTL has an effect in a particular tissue.

Concepts: Gene, Genetics, Gene expression, Effect size, Meta-analysis, Technology, Gene V. Glass


Objectives This review aimed to quantify suicide risk among agricultural, forestry, and fishery workers and study potential variations of risk within this population. Methods We conducted a systematic literature review and meta-analysis from 1995 to 2016 using MEDLINE and following the PRISMA guidelines. A pooled effect size of suicide risk among the population of interest was calculated using meta-analysis. Subgroup analyses were conducted to investigate whether effect size differed according to population or study characteristics. Meta-regression was used to identify sources of heterogeneity. Results The systematic review identified 65 studies, of which 32 were included in the meta-analysis. Pooled effect size was 1.48 [95% confidence interval (CI) 1.30-1.68] representing an excess of suicide risk among the population of interest. Subgroup analysis showed that this effect size varied according to geographic area, with a higher effect size in Japan. The following study characteristics were found to contribute to the between-study variance: reference group, measure of effect size, and study design. Conclusions Our findings suggest an excess of suicide risk among agricultural, forestry, and fishery workers and demonstrated that this excess may be even higher for these groups in Japan. This review highlights the need for suicide prevention policies focusing on this specific population of workers. More research is also needed to better understand the underlying factors that may increase suicide risk in this population.

Concepts: Medical statistics, Systematic review, Following, Confidence interval, Normal distribution, Effect size, Meta-analysis, Gene V. Glass


Whether spanking is helpful or harmful to children continues to be the source of considerable debate among both researchers and the public. This article addresses 2 persistent issues, namely whether effect sizes for spanking are distinct from those for physical abuse, and whether effect sizes for spanking are robust to study design differences. Meta-analyses focused specifically on spanking were conducted on a total of 111 unique effect sizes representing 160,927 children. Thirteen of 17 mean effect sizes were significantly different from zero and all indicated a link between spanking and increased risk for detrimental child outcomes. Effect sizes did not substantially differ between spanking and physical abuse or by study design characteristics. (PsycINFO Database Record

Concepts: Medical statistics, Child, Effect size, Meta-analysis, Abuse, Source, Gene V. Glass


BACKGROUND: This study aimed to systematically review the evidence from randomized controlled trials (RCTs) and to conduct a meta-analysis of the effects of yoga on physical and psychosocial outcomes in cancer patients and survivors. METHODS: A systematic literature search in ten databases was conducted in November 2011. Studies were included if they had an RCT design, focused on cancer patients or survivors, included physical postures in the yoga program, compared yoga with a non-exercise or waitlist control group, and evaluated physical and/or psychosocial outcomes. Two researchers independently rated the quality of the included RCTs, and high quality was defined as >50% of the total possible score. Effect sizes (Cohen’s d) were calculated for outcomes studied in more than three studies among patients with breast cancer using means and standard deviations of post-test scores of the intervention and control groups. RESULTS: Sixteen publications of 13 RCTs met the inclusion criteria, of which one included patients with lymphomas and the others focused on patients with breast cancer. The median quality score was 67% (range: 22–89%). The included studies evaluated 23 physical and 20 psychosocial outcomes. Of the outcomes studied in more than three studies among patients with breast cancer, we found large reductions in distress, anxiety, and depression (d = -0.69 to -0.75), moderate reductions in fatigue (d = -0.51), moderate increases in general quality of life, emotional function and social function (d = 0.33 to 0.49), and a small increase in functional well-being (d = 0.31). Effects on physical function and sleep were small and not significant. CONCLUSION: Yoga appeared to be a feasible intervention and beneficial effects on several physical and psychosocial symptoms were reported. In patients with breast cancer, effect size on functional well-being was small, and they were moderate to large for psychosocial outcomes.

Concepts: Cancer, Systematic review, Randomized controlled trial, Pharmaceutical industry, Clinical research, Effect size, Meta-analysis, Gene V. Glass


The (Basden, Basden, Bryner, & Thomas, 1997) is the most widely cited theoretical explanation for why the memory performance of collaborative groups is inferior to the pooled performance of individual group members remembering alone (i.e., collaborative inhibition). This theory also predicts that several variables will moderate collaborative inhibition. This meta-analysis tests the veracity of the theory by systematically examining whether or not these variables do moderate the presence and strength of collaborative inhibition. A total of 75 effect sizes from 64 studies were included in the analysis. Collaborative inhibition was found to be a robust effect. Moreover, it was enhanced when remembering took place in larger groups, when uncategorized content items were retrieved, when group members followed free-flowing and free-order procedures, and when group members did not know one another. These findings support the retrieval strategy disruption hypothesis as a general theoretical explanation for the collaborative inhibition effect. Several additional analyses were also conducted to elucidate the potential contributions of other cognitive mechanisms to collaborative inhibition. Some results suggest that a contribution of retrieval inhibition is possible, but we failed to find any evidence to suggest retrieval blocking and encoding specificity impact upon collaborative inhibition effects. In a separate analysis (27 effect sizes), moderating factors of postcollaborative memory performance were examined. Generally, collaborative remembering tends to benefit later individual retrieval. Moderator analyses suggest that reexposure to study material may be partly responsible for this postcollaborative memory enhancement. Some applied implications of the meta-analyses are discussed. (PsycINFO Database Record

Concepts: Scientific method, Memory, Hypothesis, Effect size, Theory, Meta-analysis, Statistical power, Gene V. Glass


IMPORTANCE Studies suggest that adolescents involved in bullying are more likely to carry weapons than their uninvolved peers. OBJECTIVE To use meta-analyses to determine whether victims, bullies, and bully-victims are more likely to carry weapons than uninvolved peers. DATA SOURCES PsycINFO, ERIC, MEDLINE, LILACS, EMBASE, and Dissertation Abstracts International were searched for relevant publications (1950 through January 2014). The reference list of a review article and reference lists of retrieved articles were checked for further relevant studies. STUDY SELECTION Studies were included if they provided an effect size comparing the weapon carrying of adolescent victims, bullies, or bully-victims with that of uninvolved peers. Studies that included individuals older than 21 years were excluded, as were studies that focused on incarcerated youth or youth diagnosed as having a psychopathologic condition. DATA EXTRACTION AND SYNTHESIS Studies were coded independently by 2 of us. The agreement rate was 93%. Effect sizes were coded that compared victims, bullies, or bully-victims with uninvolved peers. Meta-analyses were based on 22 studies for victims (n = 257 179), 15 studies for bullies (n = 236 145), and 8 studies for bully-victims (n = 199 563). MAIN OUTCOMES AND MEASURES This study focused on weapon carrying among adolescents. Hypotheses were formulated before the study. RESULTS Victims (odds ratio [OR], 1.97; 95% CI, 1.62-2.39), bullies (OR, 3.25; 95% CI, 2.72-3.89), and bully-victims (OR, 4.95; 95% CI, 3.77-6.50) were more likely to carry weapons than uninvolved peers. Analyses provided no indication of publication bias. Studies conducted in the United States found stronger relations between being a bully-victim and weapon carrying (OR, 7.84; 95% CI, 6.02-10.21) than studies from other countries (OR, 3.62; 95% CI, 2.30-5.68; Q1 = 8.401; P = .004). CONCLUSIONS AND RELEVANCE Involvement in bullying as a victim, bully, or bully-victim is related to weapon carrying.

Concepts: Medical statistics, Systematic review, Odds ratio, Effect size, Meta-analysis, Bullying, Gene V. Glass


The purpose of this study is to examine the effectiveness of surgical safety checklists on teamwork, communication, morbidity, mortality, and compliance with safety measures through meta-analysis. Four meta-analyses were conducted on 19 studies that met the inclusion criteria. The effect size of checklists on teamwork and communication was 1.180 (p = .003), on morbidity and mortality was 0.123 (p = .003) and 0.088 (p = .001), respectively, and on compliance with safety measures was 0.268 (p < .001). The results indicate that surgical safety checklists improve teamwork and communication, reduce morbidity and mortality, and improve compliance with safety measures. This meta-analysis is limited in its generalizability based on the limited number of studies and the inclusion of only published research. Future research is needed to examine possible moderating variables for the effects of surgical safety checklists.

Concepts: Medical statistics, Effect, Effectiveness, Effect size, Meta-analysis, Gene V. Glass


Vertical jump performance is one of the key factors in basketball. In order to determine the effectiveness of previously published interventions and their influencing factors we performed a meta- analysis. A computerized search was conducted using the databases PubMed (1966), Web of Science (1900), SPORTDiscus™ (1975),Medline (1966) and SportPilot (2008). Studies involving healthy male or female basketball players at any age and performance level were included. All trials had to investigate the benefits of resistance training programs on jumping performance in basketball players and provide a control group. The effect size (ES) was computed and the relationship between ESs and continuous variables was examined by meta-regressions, whereas subgroup meta- analyses and z-tests were used to assess the impact of categorical moderator variables. The meta-analysis included 14 studies with 20 subgroups and a total of 37 outcomes. A total of 399 participants were examined, n = 157 served as control and n = 242 took part in particular training interventions. The overall weighted ES of 0.78 (95% CI 0.41, 1.15) was significantly greater than zero (p < 0.001). None of the categorical moderator variables affected the training effect. However, positive correlations were found for training duration (r = 0.68 ; p = 0.02). The present meta- analysis demonstrates that resistance training throughout the year, using bodyweight or external weight, significantly improves vertical jump performance in healthy basketball players. Since vertical jump improvements were independent of intervention period but dependent on the duration of each individual training session the total training amount should be based on longer training sessions.

Concepts: Effect, Effectiveness, Effect size, Meta-analysis, Gene V. Glass, Vertical jump, Volleyball, Basketball statistics