Day-by-Day and Cumulative ILI Burden
Day-by-day ILI burden was defined as the residual variance in behavior on days −4 to +9 that was not accounted for in the baseline model and was computed separately for each of the 5 Fitbit features examined in this study. Cumulative ILI burden was calculated as the sum of residuals across days −4 to +9. Missing residuals were imputed with an individual-level exponentially weighted rolling mean for the purpose of computing only the cumulative ILI burden. The cumulative ILI burden was computed for the total number of steps and total sleep duration, as a cumulative sum would not have a meaningful interpretation for the other features. Our original analyses included 2 other aggregate metrics for ILI burden: the sum of residuals across days −1 to +1 and the residual on day 0 only. These results were omitted in the interest of reducing redundancy, as they closely mirrored the results of the cumulative burden across days −4 to +9. However, 