Of the total subject variance among the 369 subjects, the day-to-day variance component ranged from 27.2% (MBP) to 58.1% (MMP), whereas the cycle-to-cycle variances ranged from 1.5% (MBP) to 16.3% (MEP).
Within-subject variance was further apportioned into cycle-to-cycle variance and day-to-day variance (Box et al. 1978).
These results suggest that, after accounting for day-to-day variance, there is little additional cycle-to-cycle variance.
Cycle-to-cycle variance is the within-subject variance remaining after day-to-day variance is calculated using the replicate samples nested within each of the three cycles.
Because day is nested within cycle, the cycle-to-cycle variance uses information from the three nested daily samples in cycles 1, 2, and 3.
Specifically, estimates of the effects of dose, elapsed time and their interaction were nearly identical, as were the estimated between-subject and within-subject between-cycle variance components.
Day-to-day variance was defined as the variance in phthalate metabolite levels between samples 1 or 2 days apart, regardless of whether they were collected in cycle 1, 2, or 3. Cycle-to-cycle variance was defined as the variance between the three cycles minus the day-to-day variances within the cycles.
The repeatability of the tested RT enzymes in reverse transcription was estimated as the standard deviation (sd) of intra-assay quantification cycle (Cq) variance, while the reproducibility (inter-assay variability) was measured as the coefficient of variation (cv) of an estimated copy number between different runs.
Both additive (predicted breeding values correlated according to the relationship matrix) and nonadditive (uncorrelated) genetic effects were included in the mixed model for ABS, with cycle-specific variance components.
Fourth, variation in menstrual cycle length and variance due to pulsatility of excretion were additional sources of error.
