n =z2Np(1-p) / z2p(1-p)+(N-1)d2
n = Sample size
Z = standard normal score at 95% of confidence interval = 1.96
d = allowance for error = 0.05
N= population size = 7165
p = proportion of high performances of VHVs in elderly care = 0.50
n =1.962(7165-)(0.5)(0.5) / 1.962(0.5)(0.5)+7164(0.05)2
n = 365
The sample size was increased by 10 % in case there were any incomplete or missing data during the collection process. The total number of sample size required in this study was at least 402.