The pooled estimates did not reveal different patterns of risk by gender, exposure definition, or reference population.
However, sensitivity analysis by exposure definition showed that living less than 20 km from nuclear power plants was associated with a significant increase in the risk of thyroid cancer in well-designed studies (summary OR = 1.75; 95% CI 1.17 2.64).
Loop diuretics were excluded from the exposure definition since these drugs are typically prescribed for different indications and are a marker of increased short-term mortality in to older adults (Glynn et al. 2001).
However, besides limitations regarding the heterogeneity and design of the analyzed studies and exposure definition, the handling of potential sources of bias and confounding, such as the healthy user effect or indication bias, limits the interpretation of these data.
The use of this exposure definition will most likely result in many more exposed subjects than would be predicted based on the reported prevalence of this problem.
The studies are ranked roughly in order of the quality of the exposure definition, with the highest quality exposure definitions towards the bottom of each plot.
According to Brinton's exposure definition, a woman could report having experienced insufficient milk supply as a reason for quitting breastfeeding in the first two weeks postpartum [18].
The methodology developed for this study consists of a data integration strategy for the THIN relational schema, and reusable modules for patient selection, event selection, event correlation and exposure definition.
*Analysis based on as treated exposure definition.
Exposure definition in all the reviewed studies was quite heterogeneous.
The third methodological issue involves the related issues of exposure definition and reference group selection.
