A drought in southern California resulted in water rationing and extensive discussion of alternative water supplies. Some people believed that this drought was the worst one ever experienced in Santa Barbara County. But was this really true? Rainfall data for a 120-year period are shown In Table E. 21.6. In order to distinguish between normal and abnormal drought periods, do the following.
(a) Consider the data before the year 1920 to be a set of “normal operating data.” Use these data to develop the tat get and control limits for a Shewhart chart. Determine if any of the data for subsequent years are outside the chart limits.
(b) Use the data prior to 1940 to construct an s chart that is based on a subgroup of 10 data points for each decade. How many chart violations occur for subsequent decades?