When determining sample size we require population proportion (p) for a dichotomous outcome that to be measured (at 95% CI , 3% error ).
If the proportion (p) is unknown a conservative estimate of .5 assumed. sometimes pilot study conducted to find a value for the proportion (p). If there is previous study we can take values for the proportion (p) from there.
I am studying vaccination pattern among nurses (yes /no). There are three studies where vaccination rate was 47%, 52% and 57% . Now which values should I choose for the proportaion (p)? 0.47 or 0.52 or 0.57 or can I simply go for an intermediate 0.5?