The type I error was taken to be α = 0.05 and the type II error was
taken to be β = 0.10, with a confidence interval of 95%, assuming
a 90% likelihood of demonstrating a 30% difference in the
TENS group. From this, improvements of 10% in interferential
current18 and 37% in TENS10 had previously been observed. To
achieve this, the sample size was set at 47 patients, supposing a
total of 150 participants.27 The same method was used to investigate
the difference between the TENS and control groups, supposing
a 90% likelihood of 33% improvement in the TENS group,
since a previous study had observed a 4% improvement in the
control group and 37% in the TENS group.10 To achieve this, the
sample size was set at 26 patients for each group, with a total of
78 participants.