Suppose a similar study is planned among women who use exogenous hormones. How many participants need to be enrolled if the mean change in log10 (plasma estradiol) is −0.08, the standard deviation of change is 0.20, and we want to conduct a two-sided test with an α level of .05 and a power of .80?

Endocrinology

A study was performed to determine the effect of introducing a low-fat diet on hormone levels of 73 postmenopausal women not using exogenous hormones [15]. The data in Table 8.25 were presented for plasma estradiol in log10 (picograms/milliliter).

Table 8.25: Change in plasma estradiol after adopting a low-fat diet

_____________________________ Estradiol log10(pg/mL)^a

Preintervention ………………………………... 0.71 (0.26)

Postintervention ………………………..…….. 0.63 (0.26)

Difference …………………………….…………...………..........

(postintervention – preintervention) …….… − 0.08 (0.20)

^aValues are mean and sd (in parentheses) for log (base 10) of preintervention and postintervention measurements and for their difference.