| Value | Category |
|---|---|
| 1 | Month and year given |
| 2 | Month and age given - year imputed |
| 3 | Year and age given - month imputed |
| 4 | Year and age given - year ignored |
| 5 | Year given - age, month imputed |
| 6 | Age given - year, month imputed |
| 7 | Month given - age, year imputed |
| 8 | None - all imputed |