Skip to main content

Advertisement

Table 3 Performance measures of survival models, with the cutoff value for predicted probability = 10%,* for the 2003 sample

From: Outcomes of prolonged mechanic ventilation: a discrimination model based on longitudinal health insurance and death certificate data

Measure Sensitivity Specificity PPV NPV
  n % (se) n % (se) n % (se) n % (se)
3-month survival 2974/2984 99.7 (0.1) 68/2639 2.6 (0.3) 2974/5545 53.6 (0.7) 68/78 87.2 (3.8)
6-month survival 2329/2360 98.7 (0.2) 207/3263 6.3 (0.4) 2329/5385 43.3 (0.7) 207/238 87.0 (2.2)
1-year survival 1762/1823 96.7 (0.4) 543/3800 14.3 (0.6) 1762/5019 35.1 (0.7) 543/604 89.9 (1.2)
2-year survival 1235/1329 92.9 (0.7) 1099/4294 25.6 (0.7) 1235/4430 27.9 (0.7) 1099/1193 92.1 (0.8)
  1. PPV: positive predictive value
  2. NPV: negative predictive value
  3. se: standard error
  4. * As 10% was chosen as the cutoff value for predicted probability, patients with a predicted probability of survival < 10% were classified as a group that would die before the end of observation period, and those with a predicted probability of survival > = 10% were classified as a group that would survive the whole observation period. By comparison of predicted outcomes with actual outcomes, we further calculated the four measures for reflecting the quality of predictions in different perspectives.
  5. The formulae for these measures are below:
  6. sensitivity = (the number of patients with a predicted probability of survival > = 10%)/(the number of patients who actually survive the whole observation period);
  7. specificity = (the number of patients with a predicted probability of survival < 10%)/(the number of patients who actually died before the end of observation period);
  8. PPV = (the number of patients who actually survive the whole observation period)/(the number of patients with a predicted probability of survival > = 10%);
  9. NPV = (the number of patients who actually died before the end of observation period)/(the number of patients with a predicted probability of survival < 10%).