REFERRAL BIAS IN ANEURYSMAL SUBARACHNOID HEMORRHAGE

The objective of this study was to assess the effect of referral bias on survival in patients with subarachnoid hemorrhage (SAH). The charac teristics of 49 patients with aneurysmal SAH from a single community w ere compared with those of 328 patients referred from outside the comm unity, all treated in the same medical care setting. In addition, refe rral patients who received surgery were compared by differential survi val analysis with those still awaiting surgery at Days 1 to 3, Days 4 to 10, and Days 11 to 15. There was a dramatic difference in the 30-da y survival rate between referral patients (83%) and community patients (59%), but most of the difference had occurred by the 2nd day after S AH. In the referral patients, the variables present at first medical a ttention that were found to have an independent effect on survival wer e clinical grade, presence of coma, number of days from SAH to referra l, diastolic blood pressure, and patient age. There was a higher survi val rate at 1 year for patients who were surgically treated compared w ith those awaiting surgery for each of the three time periods. Patient s who underwent early surgical treatment had a 1-year survival rate al most identical to that of patients with late surgery. Referral patient s had a better early survival rate than did community patients because the referral group did not include patients who died and some who wer e in poor clinical condition before the opportunity for referral. The differential survival analysis described provides a new method for est imating survival for treated and untreated patients with SAH.