Lashner 1990.

Methods	Retrospective cohort study
Participants	186 patients with extensive ulcerative colitis of at least 8 years duration 91 patients have been undergoing surveillance and 95 had not Total colectomy was advised when cancer, high grade dysplasia or low grade dysplasia associated with a mass was found
Interventions	Colonoscopic surveillance versus no surveillance
Outcomes	1. Survival 2. Death 3. Cancer detection 4. Colectomy rates
Notes	Attempts to control for bias: 1. Statistical analysis: crude analyses were performed using Kaplan‐Meier product‐limit survival curves and curves were compared with the log rank test Differences in entry variables between the two groups were adjusted to remove confounding effects (age at symptom onset, sex, and duration of disease) using a Cox proportional hazards model 2. The cancer surveillance program recommended yearly colonoscopy with biopsy Patients were excluded if they were referred with cancer, if cancer was found at first evaluation or if no follow‐up information was obtained Controls were excluded if cancer was found on initial referral