Sample size
The sample size for each group was determined by using the statistical formula for comparison of proportions as follows:
n= 1/ ((1-f)) × (2×〖(Z_α+Z_β) 〗2×P×(1-P))/〖(P_0-P_1)2
Where n = minimum sample size
Po = the proportion of participants in the control group that was expected to develop respiratory
morbidity. In a study by Porto et al 23% (0.23) was reported.
P1 = the proportion of participants in the experimental group that was expected to exhibit the
outcome of interest which is respiratory morbidity. A reduction to 10% (0.10) will be
considered clinically significant in this study.
Zα = was determined from a statistical table based on the value of the level of significance. For
this study, it was set at 0.05. Therefore, Zα= 1.96.
Zβ = was determined from a statistical table based on the acceptable power of comparison
between 2 groups. For this study, power of 80% (0.80) was used, therefore Zβ= 0.84.
f = was the proportion of study participants who are expected to be lost to follow up. For this
study f = 10% (0.1)
n = 49.1
Each group was rounded up to 50.