Question

An epidemiologist is worried about the prevalence of the flu in East Vancouver and the potential shortage of vaccines for the area. She will need to provide a recommendation for how to allocate the vaccines appropriately across the city. She takes a simple random sample of 338 people living in East Vancouver and finds that 35 have recently had the flu. Suppose that the epidemiologist wants to re-estimate the population proportion and wishes for her 95% confidence interval to have a margin of error no larger than 0.04. How large a sample should she take to achieve this?

Answer 1

Refer Standard normal table/Z-table or use excel function "=NORM.S.INV((1-0.025))" to find the Z-value.

Plug in all the calculated values in the above formula.

Round the value to the nearest whole number.