| Value | Category | 
|---|---|
| 1 | Wave 1 (14/5/2020-8/7/2020) | 
| 2 | Wave 2 (16/7/2020-18/9/2020) | 
| 3 | Wave 3 (28/9/2020-30/11/2020) | 
| 4 | Wave 4 (15/1/2021-25/3/2021) | 
| 2147483622 | Don't know | 
| 2147483623 | Refused to answer | 
| 2147483624 | Outlier set to missing | 
| 2147483625 | Inconsistency set to missing | 
| 2147483647 | Not applicable |