Table 4.
Skyn detection of drinking and non-drinking days compared to SCRAM and self-report
| Detection rates | Skyn versus self-report | SCRAM versus self-reporta |
|---|---|---|
| True positive [n (%)]b | 91 (32.3%) | 35 (34.0%) |
| False positive [n (%)]c | 16 (5.7%) | 5 (4.9%) |
| True negative [n (%)]d | 102 (36.2%) | 42 (40.8%) |
| False negative [n (%)]e | 73 (25.9%) | 21 (20.4%) |
| False positive rate (%)c | 13.6% | 10.6% |
| False negative rate (%)e | 44.5% | 37.5% |
| Sensitivity (%)f | 55.5% | 62.5% |
| Specificity (%)g | 86.4% | 89.4% |
| Positive predictive value (%)h | 85.0% | 87.5% |
| Negative predictive value (%)i | 58.3% | 66.7% |
For comparisons with SCRAM data, participants with missing SCRAM data due to device malfunction were excluded (n = 4), such that, for self-report, there were 56 drinking days, 47 non-drinking days, and 2 days with missing data.
True positives (TP) occur when the test measure (e.g., Skyn) detects a drinking day that corresponds with a drinking day based on the reference measure (i.e., self-report), excluding missing data.
False positives (FP) occur when the test measure detects a drinking day that corresponds with a non-drinking day based on the reference measure, excluding missing data. The false positive rate is the proportion of days incorrectly identified as drinking days by the test measure versus the reference measure and was calculated as: FP/(FP + TN).
True negatives (TN) occur when the test measure detects a non-drinking day that corresponds with a non-drinking day based on the reference measure, excluding missing data.
False negatives (FN) occur when the test measures detect a non-drinking day that corresponds with a drinking-day based on the reference measure, excluding missing data. The false negative rate is the proportion of days incorrectly identified as non-drinking days by the test measure versus the reference measure and was calculated as: FN/(FN + TP).
Sensitivity is the proportion of test-measured drinking days detected by the reference measure and was calculated as: TP / (TP + FN).
Specificity is the proportion of test-measured non-drinking days detected by the reference measure and was calculated as: TN / (TN + FP).
Positive predictive value is the likelihood that a day classified as a drinking day by the test measure was a drinking day as defined by the reference measure and was calculated as: TP/(TP + FP).
Negative predictive value is the likelihood that a day classified as a non-drinking day by the test measure was a non-drinking day as defined by the reference measure and was calculated as: TN/(TN + FN).