Using a longitudinal dataset linking biometric and survey data from several cohorts of young adults before and during the COVID-19 pandemic (N=682), we document large disruptions to physical activity, sleep, time use, and mental health. At the onset of the pandemic, average steps decline from 10,000 to 4,600 steps per day, sleep increases by 25 to 30 min per night, time spent socializing declines by over half to less than 30 min, and screen time more than doubles to over 5 h per day. Over the course of the pandemic from March to July 2020 the proportion of participants at risk for clinical depression ranges from 46% to 61%, up to a 90% increase in depression rates compared to the same population just prior to the pandemic. Our analyses suggest that disruption to physical activity is a leading risk factor for depression during the pandemic. However, restoration of those habits through a short-term intervention does not meaningfully improve mental well-being.

We are grateful to Tom Amadio and the Chicago Heights teachers union. Matt Davis, Sean Golden, Phuong Ta and Wooju Lee provided exceptional research assistance. Financial support from the Broad Foundation (Fryer) and the Kenneth and Anne Griffin Foundation is gratefully acknowledged. The usual caveat applies. Financial support from the Broad Foundation (Fryer) and the Kenneth and Anne Griffin Foundation is gratefully acknowledged. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research. NBER working papers are circulated for discussion and comment purposes. They have not been peerreviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.

Experimental economics represents a strong growth industry. In the past several decades the method has expanded beyond intellectual curiosity, now meriting consideration alongside the other more traditional empirical approaches used in economics. Accompanying this growth is an influx of new experimenters who are in need of straightforward direction to make their designs more powerful. This study provides several simple rules of thumb that researchers can apply to improve the efficiency of their experimental designs. We buttress these points by including empirical examples from the literature.

COVID-19 has affected daily life in unprecedented ways. Using a longitudinal dataset linking biometric and survey data from several cohorts of young adults before and during the pandemic (N=685), we document large disruptions to physical activity, sleep, time use, and mental health. At the onset of the pandemic, average steps decline from 9,400 to 4,600 steps per day, sleep increases by about 25-30 minutes per night, time spent socializing declines by over half to less than 30 minutes, and screen time more than doubles to over 5 hours per day. The proportion of participants at risk of clinical depression increases to 65%, over twice the rate in the same population prior to the pandemic. Our analyses suggest that disruption to physical activity is a leading risk factor for depression during the pandemic. However, restoration of those habits-either naturally or through policy intervention-has limited impact on restoring mental well-being. * Following the norms of Economics, authorship is alphabetical. All authors contributed to the project equally. We thank Ben Schenck and William Wang for excellent research assistance

Experimental economics represents a strong growth industry. In the past several decades the method has expanded beyond intellectual curiosity, now meriting consideration alongside the other more traditional empirical approaches used in economics. Accompanying this growth is an influx of new experimenters who are in need of straightforward direction to make their designs more powerful. This study provides several simple rules of thumb that researchers can apply to improve the efficiency of their experimental designs. We buttress these points by including empirical examples from the literature.