The table below, from Lucas (1985)9 , shows the number of accidents occurring per quarter (three months), over a 10-year period, at a DuPont company facility. The data set is divided into two periods: Period I for the ?rst ?ve-year period of the study; Period II, for the second ?ve-year period.
|
5
|
5
|
10
|
8
|
3
|
4
|
2
|
0
|
|
4
|
5
|
7
|
3
|
1
|
3
|
2
|
2
|
|
2
|
8
|
6
|
9
|
7
|
7
|
1
|
4
|
|
5
|
6
|
5
|
10
|
1
|
2
|
2
|
1
|
|
6
|
3
|
3
|
10
|
4
|
4
|
4
|
4
|
(i) Perform appropriate tests to con?rm or refute the hypothesis that the true population mean number of accidents in the ?rst period is 6, while the same popu- lation parameter was halved in the second period.
(ii) Separately test the hypothesis that there is no signi?cant difference between the mean number of accidents in each period. State any assumptions needed to answer these questions.