Another strategy suggested by a meta-analysis is caution in the use of small and non-randomised clinical trials because of their demonstrated high susceptibility to error and bias.

Observational studies included in the meta-analysis that were conducted prior to the introduction of highly active antiretroviral therapy in 1996 demonstrated a statistically significant protective effect for circumcised MSM against HIV infection.

This meta-analysis found that long-term use of benzodiazepines was associated with moderate to large adverse effects on all areas of cognition, with visuospatial memory being the most commonly detected impairment.

However, this meta-analysis included two large studies of smokers, so it is not clear that the results apply to the general population.

However, a 2007 meta-analysis concluded that " pair programming is not uniformly beneficial or effective " because many other factors besides the choice of whether to use pair programming have large effects on the outcome of a programming task.

A meta-analysis of several small studies does not predict the results of a single large study, especially in a field like medicine where results are truly unpredictable.

The results of the meta-analysis found that “ music therapy with these clients has a highly significant, medium to large effect on clinically relevant outcomes .” More specifically, music therapy was most effective on subjects with mixed diagnoses.

A large meta-analysis suggested that approximately one-third of death certificates are incorrect and that half of the autopsies performed produced findings that were not suspected before the person died.

According to a meta-analysis in the Cochrane Collaboration, two large trials in Russia and Shanghai found no beneficial effects of screening by breast self-examination " but do suggest increased harm in terms of increased numbers of benign lesions identified and an increased number of biopsies performed.

Furthermore a 2003 meta-analysis of affective disorders, major depressive disorder and bipolar disorder, found a little association to the intron 2 VNTR polymorphism, but the results of the meta-analysis depended on a large effect from one individual study.

Daniel Isenberg ’ s 1986 meta-analysis of the data gathered by both the persuasive argument and social comparison camps succeeded, in large part, in answering the questions about predominant mechanisms.

* A 2009 meta-analysis of nine studies published from 1987 – 2007 concluded that EIBI has a " large " effect on full-scale intelligence and a " moderate " effect on adaptive behavior in autistic children.

A 2009 meta-analysis of six studies found large variations of effectiveness, with a trend towards a reduction of spasticity.

However, the development of statistical techniques such as meta-analysis allowed large samples to be assembled from smaller studies, revealing that apparent validity variations reflected statistical artifacts.

A large meta-analysis from Johns Hopkins University published in Neurosurgery concluded that " there is no clear consensus in these two studies or in the 45 observational studies included.

In a meta-analysis, effect sizes that represent, for example, the differences between treatment groups in a set of similar experiments, are averaged to obtain a single aggregate value representing the best estimate of the effect of treatment.

Personality and attitudinal effects have shown greater predictability, with meta-analysis of parapsychological databases showing the sheep-goat effect, and other traits, to have significant and reliable effects over the accumulated data.

In a meta-analysis of these experiments published in the British Journal of Psychology in 2004, researchers found that there was a small but significant overall DMILS effect.

Selective reporting has a compounded effect on meta-analysis, which is a statistical technique that aggregates the results of many studies in order to generate sufficient statistical power to demonstrate a result that the individual studies themselves could not demonstrate at a statistically significant level.

There is clear evidence for the effectiveness of group psychotherapy for depression: a meta-analysis of 48 studies showed an overall effect size of 1. 03, which is clinically highly significant.

Similarly, a meta-analysis of five studies of group psychotherapy for adult sexual abuse survivors showed moderate to strong effect sizes, and there is also good evidence for effectiveness with chronic traumatic stress in war veterans.

Mediating the effect of self-care management intervention in type 2 diabetes: A meta-analysis of 47 randomised controlled trials.

In its simplest form, this is normally by identification of a common measure of effect size, of which a weighted average might be the output of a meta-analysis.

More generally there are other differences between the studies that need to be allowed for, but the general aim of a meta-analysis is to more powerfully estimate the true effect size as opposed to a less precise effect size derived in a single study under a given single set of assumptions and conditions.

The advantages of meta-analysis ( e. g. over classical literature reviews, simple overall means of effect sizes etc.

* MIX 2. 0 Professional Excel addin with Ribbon interface for meta-analysis and effect size conversions in Excel ( free and commercial versions ).

A 2001 meta-analysis of clinical trials with placebo groups and no-treatment groups found no evidence for a placebo effect on objectively measured outcomes and possible small benefits in studies with continuous subjective outcomes ( particularly pain ).

) re-analysed the same data from the 2001 meta-analysis and concluded that the placebo effects for objective symptom measures are comparable to placebo effects for subjective ones and that the placebo effect can exceed the effect of the active treatment by 20 % for disorders amenable to the placebo effect, a conclusion which Hróbjartsson & Gøtzsche described as " powerful spin ".

In 1998, a meta-analysis of published antidepressant trials found that 75 % of the effectiveness of anti-depressant medication is due to the placebo effect and other non-specific effects, rather than the treatment itself.

" The effect of full-day kindergarten on student achievement: A meta-analysis.

Because narrative reviews examine significance tests rather than effect sizes, Hwang and Jeong ( 2009 ) conducted a meta-analysis of 46 knowledge gap studies.

A 2011 meta-analysis of studies of the bystander effect reported that " The bystander effect was attenuated when situations were perceived as dangerous ( compared with non-dangerous ), perpetrators were present ( compared with non-present ), and the costs of intervention were physical ( compared with non-physical ).

" A recent meta-analysis in JAMA suggested that supplementation with combinations of antioxidant vitamins ( beta-carotene, vitamin A, and vitamin E ) may increase mortality, although with respect to beta-carotene this conclusion may be due to the known harmful effect in smokers.

A comprehensive meta-analysis of the subject published in 2007 supports the existence of the correlation, and concluded that these discrepancies could be resolved when sample size and study design are taken into account.

A meta-analysis of 49 studies since 1980 found that, contrary to de Lacoste-Utamsing and Holloway, no sex difference could be found in the size of the corpus callosum, whether or not account was taken of larger male brain size.

Among other uses, effect size measures play an important role in meta-analysis studies that summarize findings from a specific area of research, and in statistical power analyses.

A meta-analysis of 208 experiments found that the mere-exposure effect is robust and reliable, with an effect size of r = 0. 26.

According to Schneider & Bryne ( 1985 ), who conducted a meta-analysis of social skills training procedures ( 51 studies ), operant conditioning procedures for training social skills had the largest effect size, followed by modeling, coaching, and social cognitive techniques.

A meta-analysis published by Adams & Engelmann ( 1996 ), a chief architect of the DI program, finds a " mean effect size average per study ...( as ) more than. 75, which confirms that the overall effect is substantial.

* A 2009 paper included a descriptive analysis, an effect size analysis, and a meta-analysis of 13 reports published from 1987 – 2007 of early intensive behavioral intervention ( EIBI, a form of ABA-based treatment with origins in the Lovaas technique ) for autism.

Operant conditioning procedures in meta-analysis had the largest effect size for training social skills, followed by modelling, coaching, and social cognitive techniques in that order.

The larger the effect size in a meta-analysis, the more evidence there is to support a claim or therapy.