| Average | Standard deviation |
Always | 8.48 | 2.063 |
For over five years | 8.63 | 1.169 |
For five years | 7.76 | 1.614 |
For three years | 6.75 | 2.271 |
For a year | 6.43 | 2.366 |
DK/NA | 5.05 | 2.455 |
Total | 7.85 | 2.71 |