Frequency and timing of environmental exposure

The timing of exposure may be critical for assessing risk. While we often use cumulative, average, or peak measures of exposure that transpire over a life course, it may be that there are critical windows of susceptibility when exposures will have their greatest effect. These windows may occur during certain ages or developmental periods, or decades prior to disease onset as a result of disease latency. In many situations, we do not have strong hypotheses of the critical time period and an exploratory approach is warranted. However, we need to be careful to acknowledge the possibility of false positives when such an exploratory approach is adopted. Therefore, future studies are often necessary to verify any temporal hypotheses that emerge from such an exploratory approach.