| Value | Category | 
|---|---|
| 0 | No data from Individual file | 
| 1 | Month and year - information complete | 
| 2 | Month and age - year imputed | 
| 3 | Year and age - month imputed | 
| 4 | Year and age - year ignored | 
| 5 | Year - age/month imputed | 
| 6 | Age - year/month imputed | 
| 7 | Month - age/year imputed | 
| 8 | None - all imputed |