10.18 Civil disorders. The years around 1970 brought unrest to many U.S. cities. Here are government data on the number of civil disturbances in each three-month period during the years 1968 to 1972.
(a) Make a line graph of these data.
(b) The data show both a longer-term trend and seasonal variation within years. Describe the nature of both patterns. Can you suggest an explanation for the seasonal variation in civil disorders?
| Period | Count | Period | Count |
|---|---|---|---|
| 1968, Jan.–Mar. | 6 | 1970, July–Sept. | 20 |
| Apr.–June | 46 | Oct.–Dec. | 6 |
| July–Sept. | 25 | 1971, Jan.–Mar. | 12 |
| Oct.–Dec. | 3 | Apr.–June | 21 |
| 1969, Jan.–Mar. | 5 | July–Sept. | 5 |
| Apr.–June | 27 | Oct.–Dec. | 1 |
| July–Sept. | 19 | 1972, Jan.–Mar. | 3 |
| Oct.–Dec. | 6 | Apr.–June | 8 |
| 1970, Jan.–Mar. | 26 | July–Sept. | 5 |
| Apr.–June | 24 | Oct.–Dec. | 5 |