Enter a value to specify the observation period (time, area, volume, number of items) for the count data. By default, Minitab uses a value of 1, but you can enter a different value to represent the sample rate of occurrence in a more useful form.
For example, inspectors inspect the number of defects in a box of towels. A towel can have more than one defect, such as 1 tear and 2 pulls (3 defects). Each box contains 10 towels. The inspectors sample 50 total boxes, and find a total of 122 defects.
- To determine the number of defects per box, the analyst uses a length of observation of 1. The rate of occurrence Minitab uses in the analysis is 122/50 = 2.44.
- To determine the number of defects per towel, the analyst uses a length of observation of 10. The rate of occurrence Minitab uses in the analysis is (122/50)/10 = 0.244.
If you enter a length of observation other than 1, convert the Hypothesized rate. For example, if your unconverted hypothesized rate is 15 defects per quarter and your length of observation is 3, enter the converted rate of 5 (15 ÷ 3) defects per month for the Hypothesized rate.