INTRODUCTION
“How big a sample do I require?” is one of the
most frequently asked questions by investigators.
Sample size calculation for a study estimating a
population prevalence has been shown in many
books (Daniel, 1999, Lwanga and Lemeshow,
1991). The aim of the calculation is to determine
an adequate sample size to estimate the
population prevalence with a good precision. It
can be calculated using a simple formula as the
calculation needs only a few simple steps.
However, the decision to select the appropriate
values of parameters required in the formula is
not simple in some situations. In this paper, we
highlight the problems commonly encountered,
and give recommendations to handle these
problems.
HOW TO CALCULATE THE SAMPLE
SIZE
The following simple formula (Daniel, 1999) can
be used: