Question: 13.14 Biologists studying the healing of skin wounds measured the rate at which new cells closed a razor cut made in the skin of an anesthetized newt. Below are the data from 18 newts, measured in micrometers per hour.

29, 27, 34, 40, 22, 28, 14, 35, 26

35, 12, 30, 23, 18, 11, 22, 23, 33

a) Make a stem plot of the healing rates (split the stems). It’s difficult to assess Normality from 18 observations, but look for outliers or extreme skewing. What do you find?

b) Scientists usually assume that animal subjects are SRSs from their species or genetic type. Treat these newts as an SRS and suppose you know that the standard deviation of healing rates for this species of newt is 8 micrometers per hour. Give a 90% confidence interval for the mean healing rate for the species.

c) A friend who knows no statistics uses the formula X-bar, (X with bar over it) ± 1.96σ / √n in a biology lab manual to get a 95% confidence interval for the mean. Is her interval wider or narrower than yours? Explain why it makes sense that higher confidence changes the length of the interval. (It is suggested that SPSS be used to solve this problem)