Meta-analysis in occupational epidemiology: a review of practice.
OBJECTIVE
To describe past practice in meta-analyses found in occupational epidemiology, identifying the major issues that should be considered by researchers planning a meta-analysis in this setting.


METHODS
An electronic search of relevant online databases was undertaken. Papers were included in the review if they contained a statistical synthesis of risks in an occupational health setting.


RESULTS
Sixty reports of meta-analyses were identified, mostly in cancer. The number of meta-analyses has increased consistently over the last 20 years. A majority of studies focused on a mean overall effect, although more than half of them also investigated heterogeneity of results. Both fixed effect and random effects meta-analysis models were employed, the former more often, and in eight studies used despite a statistically significant test for heterogeneity. A large proportion of the meta-analyses included different effect measures in the statistical synthesis, for example, including standardized mortality ratios (SMRs) and standardized incidence ratios. Most meta-analyses limited to a single type of effect measure focused on SMRs. The vast majority of meta-analyses combined all studies regardless of variation in the extent of information on exposures.


CONCLUSIONS
Meta-analyses in occupational epidemiology should properly explore and incorporate heterogeneity among studies. The meta-SMR is an important construct in this field, evidenced by a large proportion of cohort studies in the meta-analyses we identified. Controversy remains over the definition and validity of the meta-SMR. In addition, several other issues, notably dealing with heterogeneity in exposure, warrant further consideration.
Public and Environmental Health Research Unit, London School of Hygiene and Tropical Medicine, London, UK. damien.mcelvenny@hse.gsi.gov.uk
Damien M
DM
McElvenny
Ben G
BG
Armstrong
Lars
L
Järup
Julian P T
JP
Higgins
D015982:Bias; D006801:Humans; D033181:Information Dissemination; D015201:Meta-Analysis as Topic; D009784:Occupational Diseases / Q000453:epidemiology*; D016273:Occupational Exposure / Q000009:adverse effects; D012107:Research Design; D013223:Statistics as Topic / Q000379:methods