DETERMINATION OF SAMPLE SIZE FOR ESTIMATION MEANS AND FOR PROPORTIONS
The objectives in interval estimation are to obtain narrow intervals with high reliability. If we look at the components of a confidence interval, we see that the wide of the interval is determined by the magnitude of the quantity
(reliability coefficient)X (standard error )
EXERCISES
6.7.1: A hospital administrator wishes to the estimate the mean weight of babies in her hospital. How large a sample of birth records should be taken if she wants a 99 percent confidence interval that is 1 pound wide ? Assume that a reasonable estimate or standard deviation is 1 pound. What sample size is required if the confidence coefficient is lowered to 0.95.
ANSWER
n= 27.16
6.7.4: For multiple sclerosis patients we wish to estimate the mean age at which the disease was first diagnosed. We want a 95 percent confidence interval that is 10 years wide. If the population variance is 90, how large should our sample be?
ANSWER
n=14
DETERMINATION OF SAMPLE SIZE FOR ESTIMATING PROPORTION
6.8.1: An epidemiologist wishes to what proportion of adults living in a large metropolitan area have subtype a hepatitis B virus determine the sample size that would be required to estimate the true proportion to within 0.03 with 95 percent confidence. In a similar metropolitan area were not available and pilot sample could not be drawn, what sample size would be required?
ANSWER
683, 1068