| Year | 2000 | 2004 | 2012 | Mean | Standard Deviation |
| Coast | 22 (12.6%) | 18 (10.4%) | 15 (8.3%) | 18.3 | 3.51 |
| Central | 35 (20.1%) | 24 (13.9%) | 23 (12.7%) | 27 | 6 |
| Eastern | 24 (13.8%) | 23 (13.3%) | 22 (12.2%) | 23 | 1 |
| Nairobi | 19 (10.9%) | 19 (10.98%) | 15 (8.3%) | 17.7 | 2.3 |
| Rift Valley | 24 (13.8%) | 28 (16.2%) | 38 (20.99%) | 30 | 7.2 |
| Nyanza | 20 (11.5%) | 23 (13.3%) | 34 (18.8%) | 25 | 7.4 |
| Western | 15 (8.62%) | 24 (13.9%) | 22 (12.2%) | 20 | 4.72 |
| North Eastern | 15 (8.6%) | 14 (8.1%) | 12 (6.6%) | 13.7 | 1.53 |
| Total | 174 | 173 | 181 | 176 | 4.35 |