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Table 1 Final baseline survey sample size calculation

From: Using Mechanical Turk to recruit participants for internet intervention research: experience from recruitment for four trials targeting hazardous alcohol consumption

  Trial 1 Trial 2 Trial 3 Trial 4
Duration of trial recruitment 3.2 h 7 days 9 days 32 days
Total # (N) of surveys accessed 1252 4943 5412 5846
Total # of surveys removed % (of N) 30.0 (381) 34.4 (1699) 36.1 (1956) 39.5 (2310)
# (n) Reasons for removal [% of n] 381 1699 1956 2310
Blank surveys 1.0% (1) 1.9% (33) 1.9% (38) 1.5% (34)
Duplicates and suspicious data a 9.2% (35) 11.8% (200) 3.6% (71) 9.5% (220)
Incomplete eligible screeners 8.9% (34) 2.8% (47) 4.1% (81) 5.4% (125)
Ineligible screeners b 50.7% (193) 54.3% (923) 65.6% (1284) 58.8% (1359)
Participants did not pass all attention checks 27.8% (106) 27.4% (466) 22.1% (432) 21.0% (485)
Participants who indicated they did not respond honestly 2.4% (9) 1.8% (30) 2.6% (50) 3.8% (87)
Final baseline survey sample size 871 3244 3456 3536
  1. a Participants who accessed the survey multiple times, but only submitted one complete survey were retained once in the final sample. Those who completed the entire survey more than once were considered to have provided suspicious data and are not included in the final sample size
  2. b Ineligible screeners refers to those who did not proceed to the baseline survey (i.e. were <18 and reported consuming alcohol less than once per week)