TABLE 3.
Shrunken Coefficients for the Variables Chosen From L1-Regularized Logistic Regression Models Predicting 6-mo favorable GOS
| Variable | Model 1 (baseline + 1 wk DRS) | Model 2 (baseline + 1 and 2 wk DRS) | Model 3 (baseline + 1, 2, and 3 wk DRS) | Model 4 (baseline + 1, 2, 3, and 4 wk DRS) |
|---|---|---|---|---|
| (Intercept) | 2.882 | 2.719 | 3.452 | 3.285 |
| IMPACT probability of poor GOS score (lab model) | −0.024 | −0.022 | −0.016 | −0.017 |
| Age (yr) | −0.030 | −0.009 | −0.022 | −0.021 |
| ISS | 0 | 0 | 0 | 0 |
| Epidural hematoma | 0.597 | 0.100 | 0.396 | 0.370 |
| Motor component of GCS (at enrollment) | 0 | 0 | 0 | 0 |
| Glasgow Coma Scale score (at enrollment), continuous | 0.022 | 0 | 0 | 0 |
| Glasgow Coma Scale score (at enrollment), categorized | ||||
| GCS > 8, reference | – | – | – | – |
| GCS 6 to 8 | 0 | 0 | 0 | 0 |
| GCS 3 to 5 | 0 | 0 | 0 | 0 |
| Marshall CT scan (ED) | ||||
| Mass lesion (evacuated/unevacuated, reference) | – | – | – | – |
| Diffuse injury 2 | 0.323 | 0 | 0 | 0 |
| Diffuse injury 3 | 0 | 0 | 0 | 0 |
| Glucose (ED), mmol/L | 0 | 0 | 0 | 0 |
| Hemoglobin (ED), g/dL | 0 | 0 | 0 | 0 |
| Male | −0.039 | 0 | 0 | 0 |
| Prehospital hypotension | 0 | 0 | 0 | 0 |
| Prehospital hypoxia | 0 | 0 | 0 | 0 |
| Intubated in ER | 0 | 0 | 0 | 0 |
| Mechanism of injury | ||||
| Assault (reference) | – | – | – | – |
| Fall/jump | 0 | 0 | 0 | 0 |
| Motor vehicle | 0 | 0 | 0 | 0 |
| Motorcycle | 0.286 | 0 | 0.271 | 0.590 |
| Other | −0.366 | 0 | 0 | 0 |
| Pupil reactivity | ||||
| Both (Reference) | – | – | – | – |
| Neither | −0.210 | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 0 |
| Subarachnoid hemorrhage | 0 | 0 | 0 | 0 |
| Surgery on admission | −0.126 | −0.204 | −0.374 | −0.358 |
| Week 1 DRS | −0.107 | 0 | 0 | 0 |
| Week 2 DRS | NA | −0.100 | 0 | 0 |
| Week 3 DRS | NA | NA | −0.149 | −0.001 |
| Week 4 DRS | NA | NA | NA | −0.159 |
These coefficients makeup the actual prediction model using the usual logistic regression equation:
logit (Prob(GOS = favorable)) =2.882 – 0.024 × (IMPACT score) – 0.030 × age + 0.597 × (epidural hematoma) + 0.022 × (GCS sum) + 0.323 × (diffuse injury 2 on Marshall CT scan) – 0.039 × male +0.286 × (motorcycle injury) –0.366 × (other mechanism of injury) – 0.210 × (neither pupil reactive) – 0.126 × (surgery on admission) – 0.107(week 1 DRS). To get the probability, we use the formula 
, where the summation is the right side of the equation just above.