Repeatability and variability of sputum parameters
| Outcome | Visit 1 (N=15) | Visit 2 (N=15) | Visit 3 (N=12) | Correlation | SD (within) | SD (between) |
|---|---|---|---|---|---|---|
| Sputum cell count per gram (×106/G) | 5.1 (1.5–21.8) | 5.5 (1.9–16.4) | 3.6 (1.9–15.7) | 0.47 (0.45–0.66) | 0.27 (0.27–0.36) | 0.31 (0.22–0.36) |
| Sputum neutrophil count (×106/G) | 4.0 (0.9–21.4) | 5.0 (1.4–15.4) | 2.9 (1.5–13.9) | 0.51 (0.48–0.71) | 0.29 (0.28–0.39) | 0.33 (0.25–0.40) |
| Sputum macrophage count (×106/G) | 0.6 (0.1–1.4) | 0.5 (0.2–1.5) | 0.6 (0.2–1.8) | 0.37 (0.16–0.58) | 0.34 (0.3–0.38) | 0.29 (0.25–0.33) |
| Sputum cell count (×106) | 8.5 (2.4–75.3) | 4.7 (2.3–29.9) | 5.7 (2.6–26.9) | 0.45 (−0.2–0.78) | 0.45 (0.37–0.53) | 0.34 (0.32–0.35) |
| Sputum neutrophil differential count (%) | 88.8 (63.8–98.2) | 88.0 (64.8–95.5) | 84.5 (66–92.5) | 0.56 (0.51–0.62) | 8.9 (8.6–10.3) | 10.1 (7.8–10.7) |
| Sputum macrophage differential count (%) | 6.2 (1.5–36.2) | 10.8 (4.0–34.5) | 15.1 (6.0–34.0) | 0.60 (0.58–0.68) | 9.0 (8.7–9.9) | 10.3 (8.3–11.1) |
Each grid of the table contains median (range) for corresponding outcome. The summaries in the columns 2–4 use untransformed values of the outcomes. The summaries in columns 5–7 use log-transformed (base 10) counts and untransformed percentiles. The correlation value characterises a strength of association between repeated measures. The SD (within) is the estimated (within-patient) SD of the difference in outcomes observed for a patient at the different visits. The SD (between) is the estimated (between patients) SD of the outcomes observed at a particular visit. The summaries in columns 5–7 are calculated over three pair-wise summaries (ie, (visit 1, visit 2), (visit 1, visit 3), (visit 2, visit 3)). The header of columns 2–4 shows number of observations for each of the visits.