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Table 1 Number of responses and its corresponding response rate obtained at each data collection phase (i.e. after the first time participants were contacted, after participants received at least one reminder letter and for the overall study)

From: Self-reported data in environmental health studies: mail vs. web-based surveys

RegionNumber of mailed letters aNumber of mailed reminders aOverall responsesResponses after first contactResponses after reminderp-value e
Number of respondentsResponse rate (%) bNumber of respondentsResponse rate (%) cNumber of respondentsResponse rate (%) d
Anholt79592227.82025.323.4< 0.001
Total310424551066 f34.364920.941717.0
  1. a Respondents estimated to be ineligible (i.e. returned letters due to invalid address and refusals due to e.g. the fact that the house is not used on a daily basis (i.e. vacation house) and rare cases of mental sickness informed by a health care assistant) are excluded from this number. In total, 75 households were considered ineligible
  2. b Response rate was calculated by dividing the total number of respondents by the number of mailed letters
  3. c Response rate was calculated by dividing the number of respondents after the first contact by the number of mailed letters
  4. d Response rate was calculated by dividing the number of respondents after a reminder letter by the number of mailed reminders
  5. e Pearson’s Chi-squared test of proportions was used to calculate the difference between the response rates for the two contact points
  6. f Besides these surveys, 13 other responses were received without the identification code and two individuals have answered both the mail and the Web version of the questionnaire. These were not considered in this study and therefore, are not considered in this analysis