Bailer and Oris 1993 report data from a study of toxic repro

Bailer and Oris (1993) report data from a study of toxic reproductive response in the aquatic organism Ceriodaphnia dubia to the herbicide nitrofen. A measure of reproductive stress in C. dubia after exposure to the chemical is offspring counts from exposed females. A decrease in mean response in the exposure group suggests a toxic response to the chemical. Data from 20 independent animals were recorded as total number of offspring for 3 broods per animal giving:

Control: 27, 32, 34, 33, 36, 34, 33, 30, 24, 31
Nitrofen: 29, 29, 20, 27, 30, 31, 30, 26, 29, 29

Assume the pooled standard deviation is 3. What is the power for these data to detect a true reduction of 2 offspring after nitrofen exposure with an ?=0.05? You can leave the strict=FALSE option (in R).
a. 0.29
b. 0.42
c. 0.66
d. 0.73
e. 0.99

and, how many samples per group would you need to have a power of 90% in order to detect a true reduction of 2 offspring after nitrofen exposure with an alpha=0.05? Use a standard deviation of 3 and the strict=FALSE option (R software).
a. 21
b. 26
c. 40
d. 49
e. 54

Solution

1) b. 0.42

2) c. 40

are correct answers !!!!