Question: A health department nutritionist, wishing to conduct a survey among a population of teenage girls to determine their average protein intake, is seeking advice of a biostatistician relative to the sample size that should be taken. Let us assume that the nutritionist would like an interval 10 grams wide; that is, the estimate should be within 5 grams of the population mean in either direction. Let’s also assume that the confidence coefficient of 0.95 is decided on and that, from past experience, the nutritionist feels that the population standard deviation is probably about 20 grams. Determine the necessary sample size.