Continuous data meta-analysis

The issue of whether sperm counts are declining has been the focus of most media attention. A debate still continues as to whether the reported changes in sperm quality are genuine. In 1992, an article described the meta analysis of available data on semen quality in normal men, taken from reports published between the period 1938-1990. This analysis showed a 50% decline in sperm concentration... 

Each trial that is to be included in the meta-analysis will provide a measure of treatment effect (difference). For continuous data this could be the mean response on the active treatment minus the mean response in the placebo arm. Alternatively, for binary data the treatment effect could be captured by the difference in the cure rates, for example, or by the odds ratio. For survival data, the hazard ratio would often be the measure of treatment difference, but equally well it could be the difference in the two-year survival rates. 

A meta-analysis for continuous data cannot be calculated unless the pertinent standard deviations are known. Unfortunately, clinical reports often give the sample size and mean ratings for the various groups but do not report the standard deviations (or standard error of the mean), which are necessary for effect size calculations. Thus, investigators should always report the indices of variability (e.g., confidence intervals, SDs) for the critical variables related to their primary hypothesis. 

Although isolated reports of psychotic delusional symptoms and depression continue to be published (404), recent controlled trials or longitudinal studies have not provided evidence of an increase in depression scores or in the rate of depression in patients treated with interferon beta (SEDA-27, 389). In a meta-analysis of seven trials in 1215 patients with relapsing remitting multiple sclerosis, the incidence of depression was 16% and did not differ between interferon-beta and controls, but the scales used to assess depression were specified in only three trials (405). Using a public reimbursement database for multiple sclerosis, the prevalence and incidence of depression and depression scores were not different in 163 patients treated with interferon beta or glatiramer, but the study was poorly controlled for potential biases (406). Overall, the current data suggest that interferon-beta is not substantially associated with depression. 

Either UFH or LMWHs should be administered to patients with non-ST-segment-elevation ACS. Therapy should be continued for up to 48 hours or until the end of the angiography or PCI procedure. In patients initiating warfarin therapy, UFH or LMWHs should be continued until the international normalization ratio (INR) with warfarin is in the therapeutic range. Data supporting the addition of UFH to aspirin stems from a meta-analysis of six randomized trials demonstrating a 33% reduction in the risk of death or MI at 6 weeks with UFH... 

Since the smaller is reciprocal of the variance, the larger is the variance, and vice versa, the consequence is that trials for which the treatment estimate has a smaller variance should be given more weight. Suppose we have a series of perfectly balanced trials, so that for trial i we have rij patients in the experimental and fij in the control group. If we perform a meta-analysis of continuous outcomes using original data and the standard linear model, then we conventionally assume that variances within strata are equal. Where that is so, the variance of the Ith treatment estimate is... 

A paste oil of the estimated composition was made up and used in hydrogenation. The total salable monophenols (b.p., 180°-205°C.) yield from this was found to be 8.5%, and a stabilized lignin tar yield from the second hydrogenator was 19% of the net organic of the lignin. In addition to the yield data, we fractionally distilled the combined monophenol cuts from the continuous runs. The m->p-cresol peak from the gas chromatograph was analyzed by IR spectroscopy and found to be 45% w-cresol and 55% p-cresol, which meant that no pure p-cresol could be obtained by fractional crystallization of the meta, para mixture. From the fractional distillation we found we could obtain most of the monophenols indicated in the gas chromatographic analysis. 

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