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	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

To the Editor: Dr de Boer and colleagues¹ performed an extensive review of an important issue for cancer survivors. They reported that cancer survivorship was significantly associated with unemployment. However, a large amount of heterogeneity was present in the analyses of this study, not only in the overall estimate but also in subgroup analyses for breast cancer, blood cancers, gastrointestinal cancers, and mixed cancer diagnoses. Heterogeneity indicates that the observed effects are more different from each other than one would expect due to chance alone.² The presence of this large heterogeneity has considerable consequences for the validity of the study conclusions.

The authors used a random-effects model for the meta-analyses, but this model cannot remove the effects of heterogeneity.³ A meta-analysis can only be performed if the included studies are similar with regard to study design, study quality, participants, interventions, and outcomes: ie, if the studies are homogeneous.² If that . . . [Full Text of this Article]

Elvira C. van Dalen, MD, PhD
e.c.vandalen@amc.uva.nl

Leontien C. M. Kremer, MD, PhD
Cochrane Childhood Cancer Group
Emma Children's Hospital/Academic Medical Center
Amsterdam, the Netherlands

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