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PAPERS: Katrina M Wyatt, Paul W Dimmock, Peter W Jones, and P M Shaughn O'Brien Efficacy of vitamin B-6 in the treatment of premenstrual syndrome: systematic review BMJ 1999; 318: 1375-1381 [Abstract] [Full text]

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PMS undefined in trials

Yogi Sehgal   (23 May 1999)

Systematic review of Vitamin B6 efficacy

Adrian Edwards   (24 June 1999)

PMS undefined in trials 23 May 1999
Yogi Sehgal terrace bay, ontario, canada Send response to journal: Re: PMS undefined in trials	Two points: 1) The term PMS was defined in the introduction, but was this definition used in the trial? Without a strict definition IN your inclusion criteria, this trial is putting apples in with the oranges. (How do we know these patients truly have PMS?) 2) The use of odds ratios and "better"/"not better" in trial allow a minimal analysis of qualitative benefits, but whether the benefit is CLINICALLY significant CANNOT be determined, nor can one say how it helps patients? (What does "better" really mean in PMS?). I am sure, however, that a drug company somewhere that makes B6 will be using these results in their advertising... :) I do hope that a good, powerful RCT is undertaken, but my bet is that it will show no effect. YS
Systematic review of Vitamin B6 efficacy 24 June 1999
Adrian Edwards Send response to journal: Re: Systematic review of Vitamin B6 efficacy	Dear Sir Wyatt et al.'s systematic review of the efficacy of Vitamin B-6 for premenstrual syndrome (PMS) is to be welcomed in tackling an important clinical problem (1). The methods used in this review, however, may have led to an over-estimate of the treatment's efficacy. This arises from the way the outcome data appear to have been extracted from primary studies for meta-analysis. The range of outcomes reported in primary studies was broad, and by implication so too was the range of assessment methods for these outcomes. Many were in the form of continuous measures (e.g. PMS symptom scores, emotional symptoms), whilst others were binary and reported the proportion of subjects showing an improvement in symptoms. The continuous outcome data appear to have been converted into such binary format to facilitate meta-analysis and calculation of odds ratio data of efficacy compared to placebo. This is not invalid, but evidence from another 'diffuse' topic systematic review we have conducted (2) suggests that effect sizes in binary outcomes are on average greater than for continuous outcomes. In that review 23 studies reported continuous outcomes and 59 reported binary outcomes (e.g. the proportion of subjects accepting treatment or modifying health behaviour). The mean effect size of binary outcomes was 0.36 and the mean effect size of continuous outcomes was 0.18 (statistically significant difference, p=0.0062). Our review also found the effect sizes of randomised controlled trials to be smaller (mean 0.24) than for other study designs (mean 0.4; statistically significant difference, p=0.0159). This latter finding is in keeping with other literature (3,4), suggesting that the pattern of effect size variations has some generalisability for other reviews. The implication is therefore that converting continuous outcome data into binary format for meta-analysis purposes may lead to an over-estimate of efficacy. It may be more appropriate to analyse the outcomes from different studies in effect size format, which allows comparison between outcomes measured on different scales (5). A true mean (to indicate efficacy) can be produced by adjusting the data to eliminate the systematic excess in effect size evident in binary data. Then health care professionals may get a more realistic impression of the treatment's efficacy relative to placebo. If the absolute changes (or equivalent 'numbers-needed-to-treat' data) were presented as well as these relative changes or comparative data, then professionals would also have information with which to assess the true or likely effect that might be expected in practice. Dr Adrian Edwards & Dr Kerenza Hood Department of General Practice University of Wales College of Medicine Llanedeyrn Health Centre Llanedeyrn Cardiff CF3 7PN Reference List 1 Wyatt KM, Dimmock PW, Jones PW, O'Brien PMS. Efficacy of Vitamin B-6 in the treatment of premenstrual syndrome: a systematic review. BMJ 1999;318:1375-81. 2 Edwards AGK, Barker J, Bloor M, Burnard P, Covey J, Hood K et al. A systematic review of risk communication - improving effective clinical practice and research in primary care. Cardiff. University of Wales College of Medicine, Department of Gener Practice. Report to NHS Executive. 1998. 3 Colditz GA, Miller JN, Mosteller F. How study design affects outcomes in comparisons of therapy. 1.Medical. Statistics in Medicine 1989;8:441- 54. 4 Sacks H, Chalmers TC, Smith H. Randomised versus historical controls for clinical trials. American Journal of Medicine 1982;72:233-8. 5 Slavin RE. Best evidence synthesis: an intelligent alternative to meta-analysis. Journal of Clinical Epidemiology 1995;48:9- 18.