Table 1.
Definitions of cortisol indices as identified in the literature search and calculated in the current samples.
| Cortisol index | Number of times used in literature | Definition/formula for current samples |
|---|---|---|
| Baseline cortisol value | 51 | Cortisol value at baseline or pre-challenge |
| 20 min cortisol value | 41a | Cortisol value at 20 min post-challenge |
| 40 min cortisol value | 41a | Cortisol value at 40 min post-challenge |
| Mean cortisol | 12 | Average cortisol values across all samples. = Σ(baseline + 20 min + 40 min)/3 |
| AUCG | 19 | Area under the curve with respect to ground. = {[(20 min value + baseline value)/2] x time} + {[(40 min value + 20 min value)/2] x time} |
| AUCI | 9 | Area under the curve with respect to increase (or change).b = {[(20 min value + baseline value)/2] x time} + {[(40 min value + 20 min value)/2] x time} – [baseline value* (time + time)] |
| AUCAB | 1 | Area under the curve above/below baseline.b = {[(20 min – baseline)/2]*time} + {[(20 min – baseline) + (40 min – baseline)/2]*time} |
| Peak | 3 | Highest cortisol value (either baseline, 20 min, or 40 min sample). |
| Minimum | 1 | Lowest cortisol value (either baseline, 20 min, or 40 min sample). |
| Maximum increase | 1 | Highest cortisol value minus lowest cortisol value. |
| Reactivity | 10 | Change in cortisol between the baseline and 40 min values. = 40 min – baseline |
| Peak reactivity | 3 | Change in cortisol between the baseline and peak values. = peak (either baseline, 20 min, or 40 min) – baseline |
| Slope | 3 | Slope of the line between baseline and 40 min cortisol value. = (40 min – baseline)/time. |
| Regression intercept (raw) | 4 | Intercept of the regression line fitted through the raw cortisol data. |
| Regression slope (raw) | 3 | Slope of the regression line fitted through the raw cortisol data. |
| Percent change | 1 | Percent change between the first and last cortisol collection. = ((40 min – baseline)/(baseline)*100) |
Note. Time values represent the time between cortisol samples, which in the current analyses equals 20 min. AUCG = area under the curve with respect to ground; AUCI = area under the curve with respect to increase; AUCAB = area under the curve above baseline.
a
Forty one of the studies in the literature search used individual time points of cortisol collection, however, these time points were not necessarily 20 and 40 min.
b
As evident from the formulas, AUCI and AUCAB are identical indices, based on different but equivalent formula.