Control Charts: Yellowstone National Park Yellowstone Park Medical Services (YPMS) provides emergency health care for park visitors. Such health care includes treatment for everything from indigestion and sunburn to more serious injuries. A recent issue of Yellowstone Today (National Park Service Publication)

indicated that the average number of visitors treated each day by YPMS is 21.7. The estimated standard deviation is 4.2 (summer data). The distribution of numbers treated is approximately mound-shaped and symmetric.

(a) For a 10-day summer period, the following data show the number of visitors treated each day by YPMS:

Day 1 2 3 4 5 6 7 8 9 10 Number treated 25 19 17 15 20 24 30 19 16 23 Make a control chart for the daily number of visitors treated by YPMS, and plot the data on the control chart. Do the data indicate that the number of visitors treated by YPMS is “in control”?

Explain your answer.

(b) For another 10-day summer period, the following data were obtained:

Day 1 2 3 4 5 6 7 8 9 10 Number treated 20 15 12 21 24 28 32 36 35 37.

Make a control chart, and plot the data on the chart.
Interpretation Do the data indicate that the number of visitors treated by YPMS is “in control” or “out of control”? Explain your answer. Identify all outof-
control signals by type (I, II, or III). If you were the park superintendent, do you think YPMS might need some (temporary) extra help? Explain.AppendixLO1