Although matching on area of residence may result in overmatching for type of water, possibly biasing relative risks toward the null, most hospital catchment areas were large enough to provide substantial variability in water sources.
Participants 4012 women aged 20-69 winvasivesive cancer diagnosed in participating centres and two controls per case individually matched on age and area of residence.
For each potential case, a control was randomly selected from the study base matched on age, gender and residential area.
The present study includes data from 1,842 RA patients and 1,038 controls, randomly selected from the study base and matched on age, sex and residential area.
Secnik et al. and Swensen et al. compared costs of care for adults with ADHD with matched controls (matched on age, sex, metropolitan statistical area, and type of insurance coverage), and both utilized privately insured claims data for the analysis.
However, the general demographics and tobacco-exposure information of subjects included in the final analysis were similar with those of people who were excluded, and all lung cancer patients and controls were matched on age, sex, and residential area, which may have minimized the selection bias and confounding factors.
In a New York study, 100 ET patients were identified from a computer database at a medical center in New York, and 143 controls were identified using random-digit dialing in the New York City metropolitan area and matched on age strata, sex, and ethnicity (Louis et al. 2003).
Cases were recruited from population-based cancer registries and controls were selected by random-digit dialing, and frequency matched on age, gender, race and SEER area [ 26].
