Does nature heal best? A contrast (optional). The researchers who carried out the study of healing in newts described in the previous exercise conjectured that healing is fastest under natural conditions. If this is true, the population mean for the 1 group (natural field level) in Table 29.5 should be larger (or less negative) than the average of the population means for the other four groups.
(a) What population contrast expresses this comparison? What null and alternative hypotheses in terms of this contrast should the researchers use to test their conjecture?
(b) Carry out the test and state your conclusion.
(c) After you see the five sample means, it is tempting to contrast the average for the 1 and 1.25 groups with the average for the other three groups. Explain carefully why this is not legitimate.
