A researcher wants to conduct a randomized experiment to examine the effect of LSD on concentrations of chemical norepinephrine (NE) in the medulla...

A researcher wants to conduct a randomized experiment to examine the effect of LSD on concentrations of chemical norepinephrine (NE) in the medulla region of the brain in rats. Half of the rats available for the study will be randomly assigned to a control group and the other half will be ex-

posed to a specific amount of LSD. Information from other studies suggests the mean concentration

of NE brain tissue of normal rats, not exposed to LSD, is about 450 ng/gm, and the population

standard deviation is about 70 ng/gm. The researcher has decided that it would important to

detect if exposure to the amount of LSD used in the study causes either a 10% increase or a 10%

decrease in NE concentration. Using a Type I error level of 0.05, the researcher wants power 0.80

of detecting an effect of this magnitude.

(a) Determine how many rats the researcher needs to have in each group.

(b) If the researcher suspected that LSD tends to increase NE concentration and planned to use

a one-tailed t-test, what would be the required number of rats?

(c) Suppose that by switching to a better supplier of rats and improving lab procedures, the

researcher could cut the population standard deviation in half, but these improvements would

double the cost of each observation. Would these measures be cost effective?