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Table 2 Sensitivity, specificity, PPV and NPVa stratified by priority level using Medical Index and RETTS-A (n = 1278)

From: A comparison of two emergency medical dispatch protocols with respect to accuracy

Priority level Sensitivity Specificity PPV NPV
Medical Index (n = 634)
 1 82.6% (76.6–87.3) 59.0% (54.3–63.5) 47.2% (76.6–87.3) 52.8% (47.5–58.0)
 2 49.7% (42.2–52.5) 38.7% (34.3–43.4) 66.1%(60.3–71.4) 33.9% (28.6–39.7)
 3 14.1% (8.0–24.0) 98.9% (97.7–99.5) 62.5% (38.6–81.5) 37.5% (18.5–61.4)
RETTS-A (n = 644)
 Red 54.0% (44.3–63.4) 83.6% (80.3–86.5) 37.8% (30.2–45.9) 62.2% (54.1–69.8)
 Red+Orangeb 78.9% (74.9–82.5) 48.0% (41.1–54.9) 77.4% (73.3–81.0) 22.6% (19.0–26.7)
 Orange 53.2% (47.9–53.9) 57.0% (51.4–62.5) 59.0% (53.4–64.3) 41.0% (35.7–46.6)
 Yellow 45.5% (37.6–53.6) 82.6% (79.0–85.6) 48.4% (40.6–56.2) 56.9% (48.9–64.5)
 Green 9.4% (4.1–2.3) 95.1% (93.0–96.6) 13.9% (6.1–28.7) 86.1% (71.3–93.9)
  1. 95% confidence intervals in ()
  2. aSensitivity was calculated as true positives/(true positives + false negatives); Specificity as true negatives/(false positives + true negatives); Positive predictive value (PPV) as true positives/(true positives + false positives); Negative predictive value (NPV) as true negatives/(true negatives + false negatives)
  3. bAlternative analysis where RETTS-A was converted from a four graded to a three graded priority protocol. The conversion was made by merging the two highest priority levels in to one single priority level (red + orange)