Formula:
n = [(z-value * sd)/E]^2
...where n = sample size, z-value will be 1.645 using a z-table to represent the 90% confidence interval, sd = 18, E = 2, ^2 means squared, and * means to multiply.
Plug the values into the formula and finish the calculation. Round your answer to the next highest whole number.
In a preliminary study, the sample standard deviation for the duration of a particular
back pain suffered by patients was 18.0 months. How large a random sample is
needed to construct a 90% confidence interval so that an estimate can be made within
2 months of the actual duratio
1 answer
1 answer