The Influence of Population Mobility on Environmental Exposure Estimates in Case-Control Studies

Music City Center 

In many studies examining environmental risk factors for disease, researchers often rely on the location at diagnosis as the geographic reference point for assessing environmental exposures. However, environmental pollutants typically exhibit continuous variation over space and time. The dynamic nature of these pollutants, combined with population mobility in the United States, suggests that for diseases with long latency periods, such as cancer, historical exposures may be more pertinent than exposures at the time of diagnosis.

In this study, we evaluated the extent to which the common assumption of no population mobility introduces bias into the estimates of the relationship between environmental exposures and long-latency health outcomes in case-control studies. We conducted a simulation study using the residential histories of a random sample from the National Institutes of Health-AARP (formerly American Association of Retired Persons) Diet and Health Study. Case-control status was simulated based on subject exposure and true exposure effects that varied over time. We then compared estimates derived from models using only the subject's location at diagnosis with estimates assuming that subjects had experienced mobility.

Our findings indicate that ignoring population mobility leads to underestimation of subject exposure, with the largest discrepancies observed at time points more distant from the study enrollment. Generally, the impact of population mobility on the bias in estimates of the exposure-outcome relationship was more pronounced when the exposures exhibited significant spatial and temporal variability. Based on our results, we recommend incorporating residential histories when environmental exposures and disease latency periods are sufficiently long for mobility to play a critical role.

Spatial Statistics

Bayesian Analysis

Environmental Health Statistics

Disease Mapping