Refer to the brain NE data of Example 7.2.1. Suppose you are planning a similar experiment; you will

study the effect of LSD (rather than toluene) on brain NE. You anticipate using a two-tailed t test at  . Suppose you have decided that a 10% effect (increase or decrease in mean NE) of LSD would be important, and so you want to have good power (80%) to detect a difference of this magnitude.

(a) Using the data of Example 7.2.1 as a “pilot study,” determine how many rats you should have in each

group. (The mean NE in the control group in Example 7.2.1 is 444.2 ng/g and the SD is = 69.6 ng/g.)

(b) If you were planning to use a one-tailed test, what would be the required number of rats?

Example 7.2.1:

For each of the following data sets, use Table 4 to bracket the two-tailed -value of the data as analyzed by the test.

Example 7.2.1:

Toluene and the Brain Abuse of substances containing toluene (for example, glue) can produce various neurological symptoms. In an investigation of the mechanism of these toxic effects, researchers measured the concentrations of various chemicals in the brains of rats that had been exposed to a toluene-laden atmosphere, and also in unexposed control rats. The concentrations of the brain chemical norepinephrine (NE) in the medulla region of the brain, for six toluene-exposed rats and five control

rats, are given in Table 7.2.1 and displayed in Figure 7.2.1.⁴  The observed mean NE in the toluene group is substantially higher than the mean in the control group One might ask whether this observed difference indicates a real biological phenomenon—the effect of toluene—or whether the truth might be that toluene has no effect and that