The five multimorbidity indices
| Multimorbidity index weights* | |||||
| Index 1—absolute count | Index 2—individual unweighted conditions | Index 3—weighted LASSO | Index 4—weighted AIC | Index 5—weighted BMA | |
| Mood disorder | 1 | 9 | 1.2 | 2.8 | 1.8 |
| Anxiety | 1 | 7.8 | – | 2.4 | – |
| Osteoarthritis | 1 | 15.3 | 5.5 | 4.7 | – |
| Rheumatoid arthritis | 1 | 3 | – | – | 2.8 |
| Other type of arthritis | 1 | 3.2 | – | 1.1 | – |
| Asthma | 1 | 2.5 | – | – | – |
| COPD | 1 | 13.8 | 3.8 | 4.5 | 4.1 |
| Hypertension | 1 | 10.6 | 3.6 | 3.3 | – |
| Heart disease | 1 | 14.6 | 7.4 | 4.6 | – |
| Angina | 1 | 4.7 | 1 | 1.5 | 4 |
| Myocardial infarction | 1 | 9.6 | 2.2 | 3.0 | 3.9 |
| Peripheral vascular disease | 1 | 10.3 | 2.1 | 3.3 | – |
| Stroke or TIA | 1 | 4 | – | – | 4 |
| Gastrointestinal ulcer | 1 | 11.9 | 2.2 | 3.7 | 2.4 |
| Bowel disorder | 1 | 5.8 | – | 1.9 | 1.9 |
| Kidney disease or failure | 1 | 13.6 | 1.7 | 4.2 | 4.5 |
| Hypothyroidism | 1 | 4.1 | – | 1.3 | 1 |
| Hyperthyroidism | 1 | 6.7 | – | 2.2 | – |
| Diabetes | 1 | 7.8 | 1.6 | 2.4 | – |
| Osteoporosis | 1 | 1.4 | – | – | 2 |
| Cataracts | 1 | 2.7 | – | – | – |
| Glaucoma | 1 | −3.2 | – | – | – |
| Macular degeneration | 1 | 1.5 | – | – | – |
| Epilepsy | 1 | 19.1 | – | 5.8 | – |
| Parkinson’s disease | 1 | 33.2 | – | 10.2 | 7.9 |
| Multiple sclerosis | 1 | 23.3 | – | 7.1 | – |
| Migraine | 1 | 1 | – | – | |
| Allergies | 1 | 2.7 | – | 1 | – |
| Skin cancer: melanoma | 1 | −6.7 | – | – | – |
| Skin cancer: non-melanoma | 1 | −2.9 | – | – | – |
| Solid cancer | 1 | 6.4 | – | 2 | 2.9 |
| Haematological and soft cancer | 1 | 30.6 | – | 9.5 | – |
| Ill-defined cancer | 1 | −5.1 | – | – | – |
| Current smoker | 1 | 4.4 | – | 1.3 | – |
| Regular drinker | 1 | −10.5 | −1.9 | −3.3 | – |
| Internal predictive validity of the regression models (in the validation dataset)†‡ | |||||
| Nagelkerke’s R2§ | 0.06 | 0.07 | 0.06 | 0.07 | 0.06 |
| C-statistic (95% CI)§ | 0.67 (0.65 to 0.68) | 0.68 (0.67 to 0.70) | 0.67 (0.65 to 0.68) | 0.68 (0.66 to 0.69) | 0.66 (0.65 to 0.68) |
| Pearson correlation (95% CI)§¶ | 0.88 (0.84 to 0.92) | 0.89 (0.85 to 0.92) | 0.77 (0.69 to 0.83) | 0.89 (0.85 to 0.92) | 0.86 (0.81 to 0.90) |
*Index 1 is based on a regression model including the absolute count of chronic conditions as a single independent variable. Index 2 is based on a regression model where each chronic condition was treated as a dichotomous independent variable. Indices 3–5 are based on regression models that began with the same independent variables as those used for index 2, but then involved variable selection using LASSO, stepwise selection based on the Akaike information criterion (AIC), or Bayesian model averaging (BMA), respectively.
†There are many estimates for each measure due to multiple imputation. We report the median estimate.
‡For the model reference model including only age and sex, R2=0.03, C-statistic=0.62 (95% CI: 0.60, 0.64), and correlation coefficient=0.83 (95% CI: 0.74, 0.89).
§These are based on the model including the index, sex, age and an interaction between age and the index.
¶Correlation between the predicted and the observed probability of the outcome, using 130 quantiles.
COPD, Chronic obstructive pulmonary disease; LASSO, least absolute shrinkage and selection operator; TIA, transient ischaemic attack.