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Table 1 Sample size calculation parameters

From: Impact of passenger engagement through road safety bus stickers in public service vehicles on road traffic crashes in Zambia: a randomized controlled trial

Za/2 Type I error 1.96
ZB Type II error 0.84
λ 0 Estimated change in the accident rate per 1000 minibuses over the 14-month period in the control arm −0.01
  Absolute difference .01
λ 1 Estimated change in the accident rate per 1000 minibuses over the 14-month period in the intervention arm −0.02
y Number of person years in each arm 116
  Number of cars assuming cars followed for 1.16 years or 14 months 954
  Number of vehicles to follow with 10% buffer per arm 1060
  1. The sample size calculation formula in Table 1 used is adopted from Hayes & Mouton (2009). A buffer of 10% was included to allow for buses that may drop out of the study during recruitment for any reason