Three sets of data on comparable situations are available as under
| Set No. | No. of data | Mean value |
Standard Deviation |
| 1. | 9 | 8 | 1.6 |
| 2. | 12 | 7 | 1.2 |
| 3. | 15 | 9 | 1.4 |
Considering all the data sets together, the overall mean value would be
1
7.24
2
7.66
3
8.08
4
8.50