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Objectively measured physical activity and fat mass in children: a bias-adjusted meta-analysis of prospective studies - PubMed

  • ️Sat Jan 01 2011

Review

Objectively measured physical activity and fat mass in children: a bias-adjusted meta-analysis of prospective studies

Desiree C Wilks et al. PLoS One. 2011.

Abstract

Background: Studies investigating the prevention of weight gain differ considerably in design and quality, which impedes pooling them in conventional meta-analyses, the basis for evidence-based policy making. This study is aimed at quantifying the prospective association between measured physical activity and fat mass in children, using a meta-analysis method that allows inclusion of heterogeneous studies by adjusting for differences through eliciting and incorporating expert opinion.

Methods: Studies on prevention of weight gain using objectively measured exposure and outcome were eligible; they were adopted from a recently published systematic review. Differences in study quality and design were considered as internal and external biases and captured in checklists. Study results were converted to correlation coefficients and biases were considered either additive or proportional on this scale. The extent and uncertainty of biases in each study were elicited in a formal process by six quantitatively-trained assessors and five subject-matter specialists. Biases for each study were combined across assessors using median pooling. Results were combined across studies by random-effects meta-analysis.

Results: The combined correlation of the unadjusted results from the six studies was -0.04 (95%CI: -0.22, 0.14) with considerable heterogeneity (I² = 78%), which makes it difficult to interpret the result. After bias-adjustment the pooled correlation was -0.01 (95%CI: -0.18, 0.16) with apparent study compatibility (I² = 0%).

Conclusion: By using this method the prospective association between physical activity and fat mass could be quantitatively synthesized; the result suggests no association. Objectively measured physical activity may not be the key determinant of unhealthy weight gain in children.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Assessment of biases for the study by Johnson et al (23).

In this study all internal biases were additive and all external biases were proportional. Internal biases were elicited from six assessors (A–F) and external biases from five assessors (G–K). Ranges indicate 67% confidence intervals for the bias, so the bias is considered twice as likely to be inside the interval as outside it. A blank indicates no bias for that category.

Figure 2
Figure 2. Adjusting for bias for the study by Johnson et al (23).

Shown is the impact on correlations (95% confidence intervals) of adjusting for bias for the assessors (A–F and G–K) separately and combined using median pooling. Values on the left hand side of the x-axis represent a negative correlation between physical activity and change in adiposity, i.e. greater baseline physical activity is related to a smaller increase in adiposity.

Figure 3
Figure 3. Random-effects meta-analyses unadjusted, adjusted for internal biases and adjusted for internal and external biases.

The six studies evaluate the prospective associations between measured physical activity and subsequent change in adiposity in children. The correlation in each source study and the combined correlation are presented, with 95% confidence intervals.

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