Full compliance rates in the written materials’ group are
expected to be around 25%. A doubling of this rate to at
least 50% is considered to be clinically relevant. Based
upon a beta of 0.90 and an alpha of 0.05 a total of 158
athletes is required divided across both study groups. In
our experience from previous comparable studies the
dropout rate during a 12 months follow-up is about
20%. This would mean that a sample of 190 athletes is
needed per group.