In a pilot survey in a developing country, an epidemiologist compared a sample of adults who were suffering from a certain neurological disease with a sample of comparable control subjects who were free of the disease. Finding of the previous study 60% subjects with the disease and 50% of the controls were involved in fishing-related occupations. If the proportion of people involved in fishing-related occupations in the entire population is similar to that observed in the pilot survey, how many subjects should be included in a larger study in each of the two groups if the epidemiologist wishes to be 90% confident of detecting a true difference between the groups at the 5% level of significance?
Solution:
The level of significance is 5% which is standard normal deviate for α = Z_((1-α)/2)=1.96
And, 90% confidence to detecting a true difference; i.e. the standard normal deviate for β = Z_((1-β) )=1.28
The subjects who have the disease (p1) =0.60 and control (p2) = 0.50