Shaft graves in ancient Greece. Refer to the American Journal of Archaeology (Jan. 2014) study of shaft graves in ancient Greece, Exercise 2.37 (p. 78). Recall that shaft graves are named for the beautifully decorated sword shafts that are buried along with the bodies. The table on p. 364 gives the number of shafts buried at each of 13 recently discovered grave sites.

1 2 3 1 5 6 2 4 1 2 4 2 9 Source: Harrell, K. “The fallen and their swords: A new explanation for the rise of the shaft graves.” American Journal of Archaeology, Vol. 118, No. 1, Jan. 2014 (Figure 1).

a. Estimate the average number of shafts buried in ancient Greece graves using a 90% confidence interval. Give a practical interpretation of the interval.

b. What assumption about the data on shaft graves is required for the inference, part

a, to be valid?