Table 2.
Performance of the Different Definitions of Multimorbidity for the Primary Outcome of Readmission and/or Prolonged Length of Stay in the Derivation and Validation Cohortsa,b
| Definition of multimorbidity | AUC (95% CI) in the derivation cohort | AUC (95% CI) in the validation cohort | Cutoff favoring sensitivityc | Cutoff favoring specificityc |
|---|---|---|---|---|
| ≥2 Body system categories and number of health conditions | 0.65 (0.643-0.651)d | 0.71 (0.706-0.715)e | ≥3 | ≥9 |
| ≥2 Body system categories and number of chronic health conditions | 0.61 (0.606-0.614)f | 0.64 (0.634-0.644)e | ≥1 | ≥6 |
| Number of distinct body system categories | 0.65 (0.649-0.656)g | 0.71 (0.700-0.709)h | ≥2 | ≥5 |
| Number of CCS categories | 0.65 (0.648-0.656)g | 0.71 (0.704-0.714)i | ≥2 | ≥7 |
| Number of health conditions | 0.65 (0.645-0.653)j | 0.71 (0.706-0.715)i | ≥3 | ≥9 |
| Number of chronic health conditions | 0.61 (0.605-0.613)k | 0.64 (0.633-0.642)e | ≥1 | ≥6 |
| Deyo-Charlson Comorbidity Index | 0.62 (0.611-0.618)f,k | 0.64 (0.637-0.646)e,l,m | NAn | ≥6 |
| Elixhauser-Van-Walraven Comorbidity Index | 0.62 (0.611-0.619)f,k | 0.65 (0.643-0.653)m | 0 | ≥6 |
AUC = area under the receiver operating characteristic curve; CCS = Clinical Classification Software; NA = not available.
Prolonged length of stay was defined as a length of stay as long as or longer than the country-specific upper quartile (75%).
The cutoff values relate to the number of items in the respective definitions of multimorbidity. We defined the lower cutoff as having a sensitivity of ≥90%. If several cutoffs met this criterion, we chose the cutoff with the best specificity. We defined the upper cutoff as having a specificity of ≥60%. If several cutoffs met this criterion, we chose the cutoff with the best sensitivity.
These AUCs were statistically significantly different (P<.05) according to DeLong test conducted separately in the derivation and validation data sets. P values adjusted for multiple comparisons using Bonferroni correction.
There was no cutoff with ≥90% sensitivity for the Deyo-Charlson Comorbidity Index except for a score of zero, which would have resulted in one group of patients only.