Sample sizes in matched samples
| Sample | n | Rubin’s R | Rubin’s B | Rubin’s B (pairs) |
| January vs February | 2004 | 1.11 | 7.97 | 11.93 |
| January vs not vaccinated | 1294 | 1.11 | 6.75 | 8.23 |
| February vs not vaccinated | 7596 | 1.20 | 15.16 | 17.09 |
Success of the propensity score matching was assessed using Rubin’s B <25%, Rubin’s R of 0.5–2 and a bias of <10% SD for each covariate.