J.N. Katz and E. Losina comment on the above letters

In their meta-analysis of the effectiveness of navigated total knee replacement, Bauwens et al. found that navigation was associated with favorable results in terms of several radiographic parameters. The data were insufficient to evaluate effects on complication rates or functional outcomes. The article stimulated the above letter from Mason et al. and a letter from Gregori and Holt13, which prompted additional letters of clarification from Bauwens et al. Caught in the crossfire, readers might well ask why a meta-analysis led to such editorial dueling. Of note, controversy over meta-analysis is long-standing14. The debates stem in part from the methodological complexity of meta-analysis, a powerful but challenging analytic technique that permits pooling of estimates across studies. We will discuss a few of the many methodological complexities of meta-analysis to put the correspondence about navigated total knee replacement in perspective. If pooling raises so many questions, why bother to pool estimates quantitatively across studies? In many reviews, the authors simply array the findings of separate studies in evidence tables without attempting to synthesize them quantitatively into single estimates of effect. A key rationale for pooling is that the available evidence may consist of small studies that show positive (or negative) effects but lack power to establish the associations with significance. Pooling these smaller studies may avoid false-negative results due to Type-II error. A useful example of this application of meta-analysis was provided by Felson and Anderson in a meta-analysis of the effect of cytotoxic therapy and corticosteroids compared with that of corticosteroids alone for patients with lupus nephritis15. Prior small studies had suggested a beneficial effect of cytotoxic therapy. The meta-analysis overcame the small sample sizes of the component studies and illustrated the beneficial effect of cytotoxic therapy across studies. Pooling also permits the investigator to …