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Table 5 Patient characteristics in the motivating example of the International Mission for Prognosis and Analysis of Clinical Trials (IMPACT) dataset with patients grouped based on having received an intracranial pressure monitor

From: Instrumental variable analysis to estimate treatment effects: a simulation study showing potential benefits of conditioning on hospital

  Intracranial pressure monitor
(n = 3009)
No intracranial pressure monitor
(n = 4543)
Age (median, IQR) 34 (23-88) 27 (20-39)
Male sex 2385 (79%) 3510 (77%)
GCS motor score (median, IQR) 4 (2-5) 4 (2-5)
Pupillary reactivity
 -Both pupils reactive 1822 (61%) 3130 (69%)
 -One pupil reactive 575 (19%) 580 (13%)
 -No pupil reactive 612 (20%) 833 (18%)
CT classificationb
 -Normal 42 (1%) 373 (8%)
 -Diffuse II 506 (17%) 62,285 (50%)
 -Diffuse III 473 (16%) 996 (22%)
 -Diffuse IV 122 (4%) 180 (4%)
 -Mass lesion 1866 (62%) 709 (16%)
tSAH 1511 (50%) 1904 (42%)
GOSa
 -Death 832 (28%) 1666 (37%)
 -Persistent vegetative state 566 (19%) 977 (22%)
 -Severe disability 559 (19%) 724 (16%)
 -Moderate disability 161 (5%) 199 (4%)
 -Good recovery 891 (30%) 977 (22%)
  1. Table presents values after data imputation. Values are presented as n (%) unless otherwise specified
  2. a GOS: Glasgow Outcome Scale as outcome after 6 months
  3. b CT classification is based on the Marshall classification. Diffuse II refers to CT abnormalities without swelling or shift; Diffuse III refers to CT abnormalities with swelling (compressed cisterns); Diffuse IV refers to CT abnormalities with a shift