There was moderate variation in the issued sample size for each wave. This varied to meet the target number of returns nationally (180,450) and at a local authority level.
The table outlining the variation in issued sample size can be seen below.
Issued sample size by wave
| Wave | Issued sample size |
| 109 | 56,876 |
| 110 | 57,063 |
| 111 | 56,967 |
| 112 | 60,595 |
| 113 | 57,083 |
| 114 | 59,827 |
| 115 | 59,547 |
| 116 | 59,212 |
| 117 | 59,874 |
| 118 | 62,438 |
| 119 | 63,109 |
| 120 | 68,125 |