Required sample size for specified margin of error. A new bone study is being planned that will measure the biomarker tartrate-resistant acid phosphatase, or TRAP. In a study of bone turnover in young women, serum TRAP was measured in 31 subjects.
The units are units per liter (U/l). The mean was 13.2 U/l with a standard deviation of 6.5 U/l. Based on these values, find the sample size required to provide an estimate of the mean TRAP with a margin of error of 1.5 U/l for 95% confidence.