Figure 1.

Adjustment of inter-visit times using a “stretch” factor. The expected inter-visit time is 90 days. In the example below, there were actually 40 days between the second and third surveys. Thus, the reported number of 30-day exposures (green dashed lines) at the third survey is lengthened by a multiplicative factor of 40/30 to represent the number of exposures since a participant’s last visit rather than the number of exposures for the past 30 days. Similarly, the fourth survey’s reported number of exposures is increased by 110/30 to represent the number of exposures since the participant’s last visit (110 days prior to the fourth survey). For participants with an inter-visit gap greater than 120 days, data were treated as a new baseline.