Meta‐Analysis of Sleep Duration and Obesity in Children: Fixed Effect Model or Random Effect Model?

Citations Over Time

Abstract

We read with interest the systematic review and meta-analysis by Li et al.1 published in the Journal of Paediatrics and Child Health. The study describes a meta-analysis which tries to show whether sleep duration is associated with higher risk of obesity. It included 12 prospective cohort studies involving about 44 200 participants. The study concluded that short sleep duration is associated with a 45% increased risk of subsequent obesity in children.1 Taking into account certain statistical issues in this meta-analysis, the pooled relative risk (RR) of the association between obesity and short sleep duration had some level of underestimation. The underestimation stemmed from a common problem in meta-analysis that the random effects model was employed in the presence of significant publication bias. The authors in the field of meta-analysis have a common conception that random effects model meta-analysis yield more conservative estimates than fixed effect model, especially when there is observable heterogeneity among studies. But, we can discuss that in the random effect model attributed weights are very similar across studies with different sample size and different precision, therefore the pooled estimation derived from a random effect model can be highly biased especially in the presence of publication bias.2, 3 In opposite direction, the fixed effect model allocate more weight to larger studies.2 In such a scenario, pooled RR from a fixed effect model is more conservative in the presence of publication bias. Therefore, we reanalyzed the paper information to estimate how selection of a random effect model in the presence of publication bias can affect Li et al.’s reported results. Contour-enhanced funnel plot was used for assessing the presence of publication bias. As Figure 1 shows, there is a strong asymmetry in the plot; studies with larger RR (and less precision) clustered at the bottom right of the pooled log RR in the plot. This result in together with significant egger's publication bias test (b = −2.41, P = 0.03) indicate observable publication bias in this study. Considering the presence of publication bias, we used a fixed effect model and the pool estimate was RR 2.14 (95% CI 2.10–2.18) (Fig. 2). Indeed, fixed effect model estimation indicates that the risk of obesity can be 200% in children with short sleep duration. But, we should bear in mind that the fixed effect model presented gives almost all weight to one study, and the pooled RR is therefore rather a report of the result of one large study (93.2% weight allocated to one cohort study in Fig. 2) than a meta-analysis of all available evidence. On the other view, we can discuss that there is little evidence for having a conclusive estimation for the association between sleep duration and obesity in children. In conclusion, our result based on fixed effect model is similar with Li et al.1 and both indicate a medium positive effect, but the two analyses disagree on the size of the pooled RR. Conclusive interpretation of the magnitude of the effect needs further large scale prospective cohort studies.

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