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Table 1 Participation and positivity rates in the first screening round and minimal detectable difference in positivity between rounds 1 and 2 at a power of 80%.

From: Evaluation design of a systematic, selective, internet-based, Chlamydiascreening implementation in the Netherlands, 2008-2010: implications of first results for the analysis

   Number invited Participation rate % (95% CI) Positivity rate % (95% CI) Detectable decline of positivity rate (in % after screening)
Amsterdam Block A 25,121 18.0 (17.5-18.5) 2.9 (2.5-3.5) Block A versus block B 0.9
  Block B 114,937 16.8 (16.6-17.0) 3.7 (3.5-4.0) Block A versus block C 1.2
  Overall 140,058 17.0 (16.8-17.2) 3.4 (3.8-0.2) Round 1 to round 2 0.5
Rotterdam Block A 17,929 14.8 (14.2- 15.3) 6.2 (5.3-7.2) Block A versus block B 1.4
  Block B 89,877 15.3 (15.0-15.5) 4.9 (4.5- 5.2) Block A versus block C 1.8
  Overall 107,806 15.2 (15.0-15.4) 5.1 (4.7-5.4) Round 1 to round 2 0.8
South Limburg* Block A 13,124 11.0 (10.5-11.5) 5.1 (4.1-6.4) Block A versus block B 1.9
  Overall (only block A in first round) Round 1 to round 2 1.2
  1. * with application of a selection based on risk scores