| Statistic | 2006–2007 cohort | 2016–2017 cohort | March–August 2020 cohort |
|---|---|---|---|
| n | 31 676 | 37 393 | 3368 |
| Median n per practice (IQR) | 18 (9–31) | 21 (11–35) | 2 (1–4) |
| ICC: null model | 0.13 | 0.08 | 0.09 |
| Median OR: null model (bootstrap 95% CI) | 1.95 (1.89 to 1.98) | 1.62 (1.59 to 1.65) | 1.72 (1.68 to 1.76) |
| ICC: COPD patient number as predictor | 0.12 | 0.08 | 0.09 |
| Median OR: COPD patient number as predictor (bootstrap 95% CI) | 1.92 (1.87 to 1.96) | 1.67 (1.63 to 1.69) | 1.72 (1.68 to 1.76) |
| OR (number of COPD patients at practice) (95% CI) | 1.01 (1.00 to 1.01) | 1.00 (1.00 to 1.00) | 1.01 (0.98 to 1.03) |
| P-value (number of COPD patients at practice) | <0.001 | 0.097 | 0.605 |
COPD = chronic obstructive pulmonary disease. ICC = intraclass correlation coefficient. IQR = interquartile range. OR = odds ratio.