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PubMed2001

Approaches to heterogeneity in meta-analysis.

This paper reviews publications from January 1999 to March 2001 on reproductive health topics that were self-identified as meta-analysis or were indexed as meta-analysis in MEDLINE. It sought to assess whether tests of statistical heterogeneity were done, whether the results were reported, and how a finding of significance for a test of statistical heterogeneity was handled and the results interpreted. The review identified some concerns. Tests of statistical heterogeneity were not done universally even though virtually all writers on the topic emphasize their importance. Even when done, results of these tests were not universally reported. Although the consensus appears to be that heterogeneity tests are conservative for meta-analysis of studies and a probability value of 0.10 is preferred, many meta-analyses used the conventional value of 0.05 without providing a reason. The rationale for the choice of a random or fixed effects model was not generally evident. The review also provided some positive models and some recommendations for assessing, reporting and exploring heterogeneity are made considering these models and the published recommendations of experts.

Female↗

PubMed2005

Investigating heterogeneity in an individual patient data meta-analysis of time to event outcomes.

Differences across studies in terms of design features and methodology, clinical procedures, and patient characteristics, are factors that can contribute to variability in the treatment effect between studies in a meta-analysis (statistical heterogeneity). Regression modelling can be used to examine relationships between treatment effect and covariates with the aim of explaining the variability in terms of clinical, methodological, or other factors. Such an investigation can be undertaken using aggregate data or individual patient data. An aggregate data approach can be problematic as sufficient data are rarely available and translating aggregate effects to individual patients can often be misleading. An individual patient data approach, although usually more resource demanding, allows a more thorough investigation of potential sources of heterogeneity and enables a fuller analysis of time to event outcomes in meta-analysis. Hierarchical Cox regression models are used to identify and explore the evidence for heterogeneity in meta-analysis and examine the relationship between covariates and censored failure time data in this context. Alternative formulations of the model are possible and illustrated using individual patient data from a meta-analysis of five randomized controlled trials which compare two drugs for the treatment of epilepsy. The models are further applied to simulated data examples in which the degree of heterogeneity and magnitude of treatment effect are varied. The behaviour of each model in each situation is explored and compared.

Anticonvulsants↗

PubMed2006

Pregnancy outcome after first-trimester exposure to metformin: a meta-analysis.

OBJECTIVE: To conduct a systematic review and meta-analysis of pregnancy outcome after metformin use for polycystic ovary syndrome (PCOS), because the efficacy of metformin has been demonstrated in the treatment of infertility caused by PCOS, whereas the fetal safety of metformin has received very little attention, and the few studies addressing this issue are limited by small sample sizes. DESIGN: Meta-analytic review. SETTING: All pertinent studies in MEDLINE and EMBASE from 1966 to September 2004. PATIENT(S): Women with PCOS or diabetes. INTERVENTION(S): Exposure to metformin in the first trimester of pregnancy. MAIN OUTCOME MEASURE(S): Major malformations. RESULT(S): Eight studies were included in the meta-analysis, with an odds ratio of 0.50 (95% confidence interval, 0.15, 1.60). After adjustment for publication bias, metformin treatment in the first trimester was associated with a statistically significant 57% protective effect. After pooling the studies, the malformation rate in the disease-matched control group was approximately 7.2%, statistically significantly higher than the rate found in the metformin group (1.7%). CONCLUSION(S): On the basis of the limited data available today, there is no evidence of an increased risk for major malformations when metformin is taken during the first trimester of pregnancy. Large studies are needed to corroborate these preliminary results.

Abnormalities, Drug-Induced↗

PubMed2003

Prevalence of hepatitis C virus infection in porphyria cutanea tarda: systematic review and meta-analysis.

BACKGROUND/AIMS: To conduct a systematic review and meta-analysis on the prevalence of hepatitis C virus (HCV) infection in porphyria cutanea tarda (PCT). METHODS: Studies evaluating prevalence of HCV infection in patients with PCT were considered. Bibliographical searches were conducted in several electronic databases. Studies comparing HCV prevalence in PCT (cases) and in a reference group (controls) were included in the meta-analysis, combining the Odds Ratios (OR) of the individual studies. RESULTS: Fifty studies including 2,167 patients were identified. Mean HCV prevalence by serology was 47%, and 50% with polymerase chain reaction (PCR). HCV prevalence markedly varied depending on the country and the type of PCT (57% in the sporadic and 26% in the familial form). Eight case-control studies were identified. Seven studies compared HCV prevalence in PCT vs. healthy controls: 40% vs. 0.24%, respectively (OR=275; 95% confidence interval=104-725). Heterogeneity disappeared when only studies evaluating HCV infection by PCR were included. CONCLUSIONS: HCV prevalence in patients with PCT is approximately 50%, much higher than that reported in general population, suggesting a possible etiopathogenic role of HCV in PCT. The striking geographical variation in this association suggests that genetic and/or environmental factors may also be involved in the pathogenesis of this disorder.

Hepatitis C↗

PubMed1999

Lipoprotein lipase mutations, plasma lipids and lipoproteins, and risk of ischemic heart disease. A meta-analysis.

BACKGROUND: We assessed in meta-analyses the effect of the Gly188Glu, Asp9Asn, Asn291Ser, and Ser447Ter substitutions in lipoprotein lipase in the heterozygous state on lipid metabolism and risk of ischemic heart disease (same order used below). METHODS AND RESULTS: In 29 separate studies, 20 903 white subjects were screened for >/=1 of these substitutions; each meta-analysis included only some of these individuals. In population-based studies, heterozygote frequencies ranged from 0.04% to 0.2%, 2% to 4%, 1% to 7%, and 17% to 22% for the respective substitutions. Postheparin plasma lipoprotein lipase activity decreased 53% (95% CI, 31% to 75%) (only 1 study), 30% (22% to 37%), and 22% (8% to 35%) and was unchanged at 4% (-10% to 19%), respectively. Plasma triglycerides increased 78% (95% CI, 64% to 92%), 20% (9% to 33%), and 31% (20% to 43%) and decreased 8% (4% to 11%), respectively. HDL cholesterol decreased 0. 25 mmol/L (0.18 to 0.32), 0.08 mmol/L (0.04 to 0.12), and 0.12 mmol/L (0.10 to 0.15) and increased 0.04 mmol/L (0.02 to 0.06), respectively. Odds ratios for ischemic heart disease were 4.9 (95% CI, 1.2 to 20) (only 1 study), 1.4 (0.8 to 2.4), 1.2 (0.9 to 1.5), and 0.8 (0.7 to 1.0), respectively. Subgroup analysis indicated that women with the Asn291Ser substitution may have an increased risk of ischemic heart disease. CONCLUSIONS: These meta-analyses suggest that compared with noncarriers, carriers of the Gly188Glu, Asp9Asn, and Asn291Ser substitutions have an atherogenic lipoprotein profile, whereas carriers of the Ser447Ter substitution have a protective lipoprotein profile. Accordingly, risk of ischemic heart disease in heterozygous carriers is increased for Gly188Glu carriers; at most, the increase is borderline for Asp9Asn and Asn291Ser carriers; and risk is possibly decreased for Ser447Ter carriers.

Apolipoprotein A-I↗

PubMed2006

Efficacy of pharmacotherapy against core traits of borderline personality disorder: meta-analysis of randomized controlled trials.

We conducted a meta-analysis of published randomized, placebo-controlled clinical trials that evaluated the effect of pharmacotherapy in patients with borderline personality disorder. Comprehensive searches of the MEDLINE, EMBASE, PsychLIT and Cochrane Central Register of Controlled Trials databases were performed using web-based search engines. Twenty articles, reporting 22 placebo-controlled comparisons, were included in the meta-analysis: eight involved antipsychotics, seven antidepressants and seven mood stabilizers. Antidepressants (four studies, standardized mean difference -0.55, 95% confidence interval -0.92, -0.17) and mood stabilizers (six studies, standardized mean difference -1.74, 95% confidence interval -2.76, -0.73) were effective against affective instability and anger, but did not produce significant benefits against impulsivity and aggression, unstable relationships, suicidality and global functioning. Antipsychotics as a class had a positive effect in terms of impulsivity and aggression (three studies, standardized mean difference -0.31, 95% confidence interval -0.63, -0.003), interpersonal relationships (three studies, standardized mean difference -0.52, 95% confidence interval -0.87, -0.17) and global functioning (seven studies, standardized mean difference -0.56, 95% confidence interval -1.00, -0.11). No difference was observed between pharmacotherapy and placebo in terms of participants leaving the study early. Pharmacotherapy can exert a modest beneficial effect on some core traits of borderline personality disorder.

Adolescent↗

PubMed1997

Use of meta-analysis as a teaching strategy in nursing research courses.

In order to become knowledgeable consumers of nursing research, nursing students must be able to critically read research and determine the study's value for nursing practice. As the number of nursing intervention studies rises and research topics are studied more extensively, the use of meta-analysis in the discipline of nursing will also increase. The same scientific rigor demanded of other types of research must be applied to meta-analysis. In this article two teaching strategies using meta-analysis are shared for sharpening both undergraduate and graduate nursing students' critiquing skills. On the undergraduate level, nursing students can assess the quality of the studies included in a particular meta-analysis. On the graduate level, students can use an appraisal checklist of criteria for evaluating the actual meta-analysis.

Clinical Competence↗

PubMed2003

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), Pearson's 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.

Humans↗

PubMed2005

A meta-analysis of outcomes of external fixation versus plate osteosynthesis for unstable distal radius fractures.

PURPOSE: External fixation and open reduction and internal fixation have been the traditional techniques for surgical fixation of unstable distal radius fractures. The existing literature has not identified which is superior, primarily because of the lack of comparative trials. We performed a comprehensive systematic review and meta-analysis of the current literature on external fixation and internal fixation of distal radius fractures to determine the dominant strategy based on available scientific evidence. METHODS: We searched MEDLINE and EMBASE for English-language articles published between 1980 and 2004 that satisfied predetermined inclusion and exclusion criteria. The outcomes of internal and external fixation were compared using continuous measures of grip strength, wrist range of motion, and radiographic alignment and categoric measures of pain, physician-rated outcome scales, and complication rates. Outcomes were pooled by random-effects meta-analysis and meta-regression analysis was used to control for patient age, presence of intra-articular fracture, duration of follow-up period, and date of publication. Sensitivity analyses were used to test the stability of the meta-analysis results under different assumptions. RESULTS: Forty-six articles were included in the review with 28 (917 patients) external fixation studies and 18 (603 patients) internal fixation studies. Meta-analysis did not detect clinically or statistically significant differences in pooled grip strength, wrist range of motion, radiographic alignment, pain, and physician-rated outcomes between the 2 treatment arms. There were higher rates of infection, hardware failure, and neuritis with external fixation and higher rates of tendon complications and early hardware removal with internal fixation. Considerable heterogeneity was present in all studies and adversely affected the precision of the meta-analysis. CONCLUSIONS: The current literature offers no evidence to support the use of internal fixation over external fixation for unstable distal radius fractures. Comparative trials using appropriately sensitive and validated outcome measurements are needed to guide treatment decisions.

Bone Plates↗

PubMed1994

Plasma levels of atrial natriuretic peptide in normal and hypertensive pregnancies: a meta-analysis.

OBJECTIVE: Our goals were (1) to use meta-analysis to determine whether pregnancy and the puerperium are accompanied by alterations in plasma atrial natriuretic peptide levels when compared with the nonpregnant state and (2) to evaluate the additional effects of hypertensive disease during pregnancy on plasma atrial natriuretic peptide levels. STUDY DESIGN: Articles measuring atrial natriuretic peptide levels during pregnancy were reviewed. Data from articles meeting inclusion criteria were abstracted, and a meta-analysis was performed with the use of the maximum likelihood methods of Jennrich and Schluchter (Biometrics 1986;42:805-20). RESULTS: The mean atrial natriuretic peptide level in nonpregnant control subjects was 28.7 pg/ml (95% confidence interval 22.5 to 36.7). The mean plasma atrial natriuretic peptide level rose 41% to 40.5 pg/ml (95% confidence interval 31.7 to 51.8) in the third trimester (p < 0.0001). It was 71.1 pg/ml (95% confidence interval 51.2 to 98.7) or 148% greater than the mean nonpregnant level during the first week post partum (p < 0.0001). Compared with levels in pregnant control subjects, plasma atrial natriuretic peptide levels increased 52% to 52.1 pg/ml (95% confidence interval 32.9 to 82.5) in women with gestational hypertension (p < 0.005) and 130% to 78.8 pg/ml (95% confidence interval 52.3 to 118.8) in women with preeclampsia (p < 0.0001). Chronic hypertension did not significantly alter atrial natriuretic peptide levels. CONCLUSIONS: The 41% increase in atrial natriuretic peptide levels in the third trimester suggests that atrial stretch receptors sense the expanded blood volume as normal to moderately increased. The rise in atrial natriuretic peptide during the first week post partum is consistent with known hemodynamic changes and suggests that atrial natriuretic peptide may be involved in the postpartum diuresis. The marked increase in plasma atrial natriuretic peptide levels observed in preeclampsia is not likely to result from elevated arterial pressures alone but may reflect underlying factors unique to this disease process.

Atrial Natriuretic Factor↗

PubMed2000

Male circumcision and risk of HIV infection in sub-Saharan Africa: a systematic review and meta-analysis.

OBJECTIVE: To systematically review studies of male circumcision and the risk of HIV-1 infection in men in sub-Saharan Africa, and to summarize the findings in a meta-analysis. DESIGN: A meta-analysis of observational studies. METHODS: A systematic literature review was carried out of studies published up to April 1999 that included circumcision as a risk factor for HIV-1 infection among men in sub-Saharan Africa. A random effects meta-analysis was used to calculate a pooled relative risk (RR) and 95% confidence interval (CI) for all studies combined, and stratified by type of study population. Further analyses were conducted among those studies that adjusted for potential confounding factors. RESULTS: Twenty-seven studies were included. Of these, 21 showed a reduced risk of HIV among circumcised men, being approximately half that in uncircumcised men (crude RR = 0.52, CI 0.40-0.68). In 15 studies that adjusted for potential confounding factors, the association was even stronger (adjusted RR = 0.42, CI 0.34-0.54). The association was stronger among men at high risk of HIV (crude RR = 0.27; adjusted RR = 0.29, CI 0.20-0.41) than among men in general populations (crude RR = 0.93; adjusted RR = 0.56, CI 0.44-0.70). CONCLUSION: Male circumcision is associated with a significantly reduced risk of HIV infection among men in sub-Saharan Africa, particularly those at high risk of HIV. These results suggest that consideration should be given to the acceptability and feasibility of providing safe services for male circumcision as an additional HIV prevention strategy in areas of Africa where men are not traditionally circumcised.

Africa South of the Sahara↗

PubMed1996

A meta-analysis of smoking prevention programs after adjustment for errors in the unit of analysis.

This article presents the results of a meta-analysis designed to test the prevailing view that we largely understand why adolescents start to smoke and how to delay it. This view has developed even though none of the major reviews of the last 12 years has adjusted for the important methodological problems that all of those reviews identified as common in the published literature. School-based smoking prevention programs based on peer or social-type programs, published between 1974 and 1991, were included in this meta-analysis. Treatment characteristics were used to predict an effect size after adjustment for study design and population characteristics, and in particular, after a post hoc correction for errors in the original unit of analysis. The results suggest that the average effect for peer or social-type programs is likely to be quite limited in magnitude, and that the reduction in smoking may be only 0.10 standard deviation units, or perhaps 5%. Even under optimal conditions, the reduction in smoking may be only 0.50 to 0.75 standard deviation units, or perhaps 20%-30%.

Adolescent↗

PubMed1991

A general parametric approach to the meta-analysis of randomized clinical trials.

Meta-analysis provides a systematic and quantitative approach to the summary of results from randomized studies. Whilst many authors have published actual meta-analyses concerning specific therapeutic questions, less has been published about comprehensive methodology. This article presents a general parametric approach, which utilizes efficient score statistics and Fisher's information, and relates this to different methods suggested by previous authors. Normally distributed, binary, ordinal and survival data are considered. Both the fixed effects and random effects model for treatments are described.

Humans↗

PubMed2001

Reporting of outcomes in arthritis trials measured on ordinal and interval scales is inadequate in relation to meta-analysis.

OBJECTIVES: To study whether the reporting of clinical outcomes in arthritis trials measured on ordinal and interval scales is adequate in relation to meta-analysis. METHODS: Systematic review of randomised trials of non-steroidal anti-inflammatory drugs in patients with rheumatoid arthritis. Optimal reporting was defined as data in the original ordered categories for global evaluation and pain, and as mean and SD for number of tender joints and grip strength, and if a visual analogue scale had been used to measure pain. RESULTS: A total of 144 trials were included. The median sample size was 60 patients. The quality of the reporting increased over time for three of the four variables. Global evaluation was optimally reported in 52 of the 127 trials (41%) in which it was recorded. Pain was optimally reported in 27 of 98 trials (28%), number of tender joints in 41 of 123 trials (33%), and grip strength in 34 of 124 trials (27%). Even if rather broad criteria are adopted, only about half of the data were reported in a potentially useful way for a meta-analysis. CONCLUSIONS: Arthritis trials have been reported inadequately in relation to meta-analysis. As most trials are underpowered, meta-analysis is indispensable and the deficit therefore needs urgent improvement. Investigators should specify a priori what constitutes an important treatment effect and report numbers of patients improved.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1997

Sensitivity and attachment: a meta-analysis on parental antecedents of infant attachment.

This meta-analysis included 66 studies (N = 4,176) on parental antecedents of attachment security. The question addressed was whether maternal sensitivity is associated with infant attachment security, and what the strength of this relation is. It was hypothesized that studies more similar to Ainsworth's Baltimore study (Ainsworth, Blehar, Waters, & Wall, 1978) would show stronger associations than studies diverging from this pioneering study. To create conceptually homogeneous sets of studies, experts divided the studies into 9 groups with similar constructs and measures of parenting. For each domain, a meta-analysis was performed to describe the central tendency, variability, and relevant moderators. After correction for attenuation, the 21 studies (N = 1,099) in which the Strange Situation procedure in nonclinical samples was used, as well as preceding or concurrent observational sensitivity measures, showed a combined effect size of r(1,097) = .24. According to Cohen's (1988) conventional criteria, the association is moderately strong. It is concluded that in normal settings sensitivity is an important but not exclusive condition of attachment security. Several other dimensions of parenting are identified as playing an equally important role. In attachment theory, a move to the contextual level is required to interpret the complex transactions between context and sensitivity in less stable and more stressful settings, and to pay more attention to nonshared environmental influences.

Adult↗

PubMed1991

[Endoscopic hemostasis for hemorrhagic gastroduodenal ulcer. Meta-analysis of randomized clinical trials].

To demonstrate the advantages of various endoscopic hemostatic methods (laser photocoagulation, electrocautery, injection therapy) for bleeding gastroduodenal ulcer in patients at high risk for continued or recurrent bleeding, a critical review of published randomized clinical trials was made with meta-analytic methods. Only the 15 clinical trials dealing either with patients with visible non bleeding vessels or spurting arterial bleeding were included. Regarding visible non bleeding vessels, the meta-analysis of five trials on electrocautery and two trials on sclerotherapy showed a significant reduction in rebleeding rates in the treatment group compared with untreated controls. The odds ratios were 4 (95 percent confidence levels (CL): 2.4-6.9) (P less than 0.001) and 6.8 (95 percent CL: 2.7-17.2) (P less than 0.001), respectively. As well, the meta-analysis of four trials on electrocautery and the two trials on sclerotherapy showed a significant reduction in the number of emergency surgical operations in the treated groups a compared with the untreated groups. The odds ratios were 5.5 (95 percent confidence levels (CL): 2.7-11.3) (P less than 0.001) and 6.1 (95 percent CL: 2.1-17.8) (P less than 0.001), respectively. Meta-analysis did not show any advantage for laser, electrocautery, or sclerotherapy in terms of mortality. Indirect meta-analysis did not reveal any difference between electrocautery and sclerotherapy. Regarding spurting arterial bleeding, meta-analysis of the two YAG laser trials, the two Argon laser trials, and the two electrocautery trials showed a significant reduction of rebleeding or continued bleeding in the treatment groups as compared with the control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Duodenal Ulcer↗

PubMed2000

[Clinical benefits of cholesterol lowering treatments. Meta-analysis of randomized therapeutic trials].

PRIMARY PREVENTION: A meta-analysis of the 7 available randomized cholesterol lowering trials (2 on statins, 2 on fibrates, 2 on resins and 1 on diet) demonstrates a significant 24% relative reduction in the frequency of fatal and non-fatal coronary events, leading to a significant 14% relative reduction in coronary disease related mortality. For total mortality, the statin trials were not comparable with other treatments where there was a trend to overmortality. With the 2 statin trials, there was a nonsignificant 13% reduction in total mortality. SECONDARY PREVENTION: A meta-analysis of the 13 available randomized trials (3 with clofribrate, 1 with gemfibrozil, 2 with nicotinic acid, and 4 with diet) showed a significant 21% reduction in the frequency of fatal and non-fatal coronary events, coronary mortality and total mortality. For total mortality, only the result of the 2 statin trials was significant (-20%). BENEFICIAL EFFECT OF STATINS, ABSOLUTE VALUES: Measured as the number of patients to treat for 5 years in order to avoid 1 event (NNT), there is a clinically pertinent benefit of secondary prevention (NNT = 15 for events, NNT = 30 for coronary mortality). The absolute value is weaker when patients with minimally elevated cholesterol levels are included. For primary prevention, the absolute value is low with NNT = 44 for events and NNT = 300 for coronary mortality. In addition, as these results were obtained in trials including populations with a much higher risk than the general French population, the absolute beneficial effect may not be pertinent in France except in high-risk patients who present, in addition to a high cholesterol level, other cardiovascular risk factors.

Anticholesteremic Agents↗

PubMed2001

Area-wide urban traffic calming schemes: a meta-analysis of safety effects.

This paper presents a meta-analysis of 33 studies that have evaluated the effects on road safety of area-wide urban traffic calming schemes. Area-wide urban traffic calming schemes are typically implemented in residential areas in towns in order to reduce the environmental and safety problems caused by road traffic. A hierarchical road system is established and through traffic is removed from residential streets by means of, for example, street closures or one-way systems. Speed reducing devices are often installed in residential streets. Main roads are improved in order to carry a larger traffic volume without additional delays or more accidents. The meta-analysis shows that area-wide urban traffic calming schemes on the average reduce the number of injury accidents by about 15%. The largest reduction in the number of accidents is found for residential streets (about 25%), a somewhat smaller reduction is found for main roads (about 10%). Similar reductions are found in the number of property damage only accidents. The results of evaluation studies are robust with respect to study design. There is no evidence of publication bias in evaluation studies. Study findings are found to have high external validity.

Accidents, Traffic↗