Grey-Seal Nursing. The average lactation (nursing) period of all earless seals is 23 days. Grey seals are one of several types of earless seals. The length of time that a female grey seal nurses her pup is studied by S. Twiss et al. in the article “Variation in Female Grey Seal (Halichoerus grypus) Reproductive Performance Correlates to Proactive-Reactive Behavioural Types” (PLOS ONE 7(11):

e49598. doi:10.1371/journal.pone.0049598). A sample of 14 female grey seals had the following lactation periods, in days. 20.2 20.9 20.6 23.6 19.6 15.9 19.8 15.4 21.4 19.5 17.4 21.9 22.3 16.4 In Exercise 9.84, you were asked to use these data to decide whether the mean lactation period of grey seals differs from 23 days. There, you were to assume that the population standard deviation of lactation periods for grey seals is 3.0 days. At the 10% significance level, do the data provide evidence against that assumption? (Note: s = 2.501.)