The reason for the observed difference in association by timing of exposure in our study is unclear.
Other studies estimated effects based on both temporal and spatial PM contrasts, where estimates were calculated for multiple geographic administrative units or at each maternal address; in these studies, exposures differed both by maternal address and by timing of the pregnancies within the study period.
High pill-years of NSAID use and breast cancer risk among premenopausal women by timing of reproductive events, the Sister Study (2003 2013).
Comparison is limited, however, by differences in enrolment criteria (larger lesions in our study), definition and timing of study endpoints.
Second, variation in the timing of study enrollment may cause selection bias even though we statistically adjusted and confirmed that the study outcome was not affected by the timing of study enrollment.
However, neither of these studies stratified by timing of cART initiation (before or during the pregnancy), which limits comparison with our study.
This study sought to compare patient characteristics, co-morbidities, mortality, and length of stay by timing of ADHF onset.
Too few studies stratified data according to the timing of vaccinations to adequately assess whether the associations differed by timing of vaccination as postulated by Classen and Classen [ 27, 28].
It is also possible that our findings are influenced by the timing of the study.
Although lifetime or 1-year prevalence of headache will not be affected much by the timing of the studies, we should be cautious in interpreting such data as recall bias may vary with timing: people tend to remember their more recent headaches.
