Table 6.
Variability in quantitative results within categories defined by individual sources of variability
| Analysis | No. of Valid Comparisons | Mean of Difference of Repeat Tests in IU/ml (95% CI) | Within-Subject SD of Variation (95% CI) | Coefficient of Variation (%) |
|---|---|---|---|---|
| Pretest storage | 14 | −0.05 (−0.09 to 0.18) | ±0.18 (0.13 to 0.27) | 4 |
| Preincubation delay (0, 6, 12 h) | 168 | −0.24 (−0.33 to −0.15) | ±0.83 (0.77 to 0.90) | 153 |
| Incubation time (16, 20, 24 h) | 100 | −0.001 (−0.01 to 0.008) | ±0.18 (0.15 to 0.20) | 49 |
| Incubation time (24, 48, 72 h) | 66 | 0.0001 (−0.02 to 0.03) | ±0.24 (0.20 to 0.29) | 21 |
| Interoperator variability | 42 | −0.05 (−0.35 to 0.26) | ±0.71 (0.57 to 0.88) | 34 |
| Blood volume | 100 | −0.11 (−0.18 to −0.04) | ±0.70 (0.61 to 0.81) | 84 |
| Plasma storage (fresh vs. −80°C) | 21 | −0.03 (−0.08 to 0.14) | ±0.37 (0.28 to 0.47) | 68 |
| Plasma storage (fresh vs. 4°C) | 288 | 0.04 (−0.01 to 0.10) | ±0.34 (0.31 to 0.37) | 57 |
| Shaking | 40 | 0.37 (−0.06 to 0.79) | ±0.97 (0.78 to 1.21) | 83 |
| ELISA repeat reading (immediate vs. 2 h) | 19 | −0.004 (−0.01 to 0.01) | ±0.02 (0.01 to 0.02) | 6 |
| Skin test boosting | 219 | 0.01 (−0.004 to 0.02) | ±0.07 (0.07 to 0.08) | 190 |