Stress/depression across the COVID-19 pandemic in Denmark

BMC Public Health

Table 1 Description of survey rounds

Survey Round	Sample Size	Response Rate	Number of responses	Sample Type	Collection period
1	8,300	0.340	2,821	Longitudinal (initial)	March 2 – April 13, 2020
2	2,818	0.550	1,549	Longitudinal	July 2 – August 01, 2020
3	8,200	0.352	2,883	Cross-sectional	September 01 – September 30, 2020
4	2,818	0.579	1,632	Longitudinal	November 04 – November 30, 2020
5	13,360	0.223	2,978	Cross-sectional	March 03 – April 24, 2021
6	2,802	0.550	1,541	Longitudinal	March 03 – April 24, 2021
7	13,375	0.286	3,821	Cross-sectional	September 14 – November 26, 2021
8	2,796	0.541	1,513	Longitudinal	November 12 – December 30, 2021
9	13,325	0.239	3,182	Cross-sectional	March 01 – April 18, 2022
10	2,781	0.337	938	Longitudinal	March 01 – April 18, 2022
Total	70,575	0.324	22,858	N/A	March 2, 2020 – April 18, 2022

Note: All data collected by Statistics Denmark with the approval of the Capital Region of Denmark’s Mental Health Services and under informed consent from the participants. Statistics Denmark randomly selected respondents (using unique personal identification numbers) from the full population aged 18–79. All respondents to Survey Round 1 were contacted on March 1st, 2020, via their official and mandatory Danish digital post-box. In subsequent rounds of the longitudinal sample, respondents to the previous round of the longitudinal sample were recontacted (using the same method), which explains the declining number of responses for the longitudinal sample. Cross-sectional samples each represent a new random draw from the population performed by Statistics Denmark; again, all respondents were contacted via the digital post-box just prior to the opening of the survey round. The total sample size reported in the bottom row of the table hence includes returning respondents; the number of unique respondents was 15,685. Decline in sample size for longitudinal sample due to outmigration and mortality.

ISSN: 1471-2458