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Table 1 Most common reasons for non-participation stated in the tick boxes and the free text field of the invitation letter

From: Results of the Cologne Corona surveillance (CoCoS) study – a prospective population-based cohort study: incidence data and potential underestimation of new SARS-CoV-2 adult infections by health authorities

  First surveillance round:
  Reasons Number of Counts Percentage of 207 stated reasons
Tick Answers Did not want to undergo saliva sampling 42 20.29%
Did not want to spend as much time on the topic 26 12.56%
Data privacy concerns 25 12.08%
Did not think the topic was important 6 2.90%
Free text field answers Medical and health issues (not associated with COVID-19) 21 10.14%
High age 13 6.28%
Longer stay outside Cologne 10 4.83%
Taking regular tests for SARS-CoV-2 infection 9 4.35%
No access to internet / No technical equipment 8 3.86%
Too much effort 8 3.86%
General criticism of the study 8 3.86%
Already vaccinated 6 2.90%
  Second surveillance round:
  Reasons Number of Counts Percentage of 96 stated reasons
Tick Answers Did not want to undergo saliva sampling 15 15.63%
Did not want to spend as much time on the topic 12 12.50%
Data privacy concerns 7 7.29
Did not think the topic was important 3 3.13%
Free text field answers Medical and health issues (not associated with COVID-19) 12 12.50%
Already vaccinated 10 10.42%
Longer stay outside Cologne 8 8.33%
Personal reasons 4 4.17%
Missed deadline for participation 4 4.17%
High age 3 3.13%
No access to internet/No technical equipment 3 3.13%
No acceptance of gender-sensitive language 3 3.13%