How It Works
Study Design
The carryover study uses a fixed 21-specimen sequence. Two specimen pools are prepared: one at a low concentration and one at a high concentration. The sequence is designed so that low specimens appear both before and after high-concentration exposures, enabling a direct comparison between contaminated and uncontaminated low-concentration measurements.
CarryoverVerificationJohn et al. (2015) / Industry standard21 specimens
| Total specimens | 21 measurements in a fixed sequence |
| Low concentration specimens | 11 total (3 baseline + 8 test) |
| High concentration specimens | 10 total |
| Sequence pattern | L, L, L, H, H, L, H, H, L, L, L, L, H, H, L, H, H, L, H, H, L |
| Baseline control | Positions 1–3 (Low specimens before any High exposure) |
| Test specimens | Low specimens in positions 6, 9–12, 15, 18, 21 (each follows at least one High specimen) |
The sequence must be run in order with no gaps. The positions of the Low specimens relative to the preceding High specimens are critical — the statistical analysis depends on which Low specimens were exposed to high-concentration carryover and which were not.
Sequence integrity is essential. Results must be entered in the exact order they were measured. Do not rearrange specimens or fill gaps with estimated values. If the run was interrupted or a result was voided, the study must be repeated from the beginning to preserve the integrity of the carryover assessment.