Kaplan-Meier survival analysis: types of censored observations

Researchers investigated if a low dose of the angiotensin converting enzyme (ACE) inhibitor ramipril reduced the incidence of cardiovascular and renal events in patients with type 2 diabetes. A randomised, double blind, parallel group trial design was used. Intervention was ramipril (1.25 mg/day) or placebo for at least three years. Participants were 4912 patients with type 2 diabetes aged over 50 years who used oral antidiabetic drugs and had persistent microalbuminuria or proteinuria. Participants received their usual treatment in addition to their allocated intervention.1

The primary outcome was cardiovascular death, non-fatal myocardial infarction, stroke, heart failure leading to hospital admission, or end stage renal failure. Participants were followed for a median of four years (range 3-6 years). Of 2443 participants randomised to ramipril, 362 (14.8%) experienced a cardiovascular or renal event, compared with 377 (15.3%) of the 2469 randomised to placebo.

Kaplan-Meier survival analysis was used to compare the treatment groups in the length of time after randomisation until first occurrence of the primary outcome. Patients who did not experience the primary outcome during follow-up had their …