estimation of sample size

Estimation of sample size : Estimation of sample size

Using Prevalence : Using Prevalence Outcome variable : underweight in PSC What is the prevalence in earlier studies / literature If not available conduct pilot study Suppose prevalence of underweight is 45% Assumptions -95% confidence interval (or) 5% level of significance This value is 1.96 (normal curve tables ) Relative precision =20% (How much expected difference from the prevalence) (Higher the prevalence- lower relative precision, usually 10%) (Lower the prevalence – higher relative precision, usually 20%)

Formula : Formula Sample size - n=Z2q/ Pe2 Where Z=1.96 P= prevalence q=1-p e= relative precision

Example : Example Prevalence of underweight (p) =45% q=1-0.45= 0.55 z=1.96 e=0.2 Then, sample size =1.96 x 1.96 x 0.55 0.45 x 0.2 x 0.2 =2.11288 =117 0.018