Critical appraisal:Baron JA, Cole BF, Sandler RS, Haile RW, Ahnen D, Bresalier R, et al 2003

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Risk of bias assessment: Randomised Controlled Trial (Cochrane risk of bias tool)

Random sequence generation
Describe the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.Jutta's question mark icon.png
Blocked randomization with the use of computer-generated random numbers was stratified according to study center, sex, and age (60 years or younger vs. older than 60 years).
What was the risk of bias from the random sequence generation?Jutta's question mark icon.png
Allocation concealment
Describe the method used to conceal the allocation sequence in sufficient detail to determine whether intervention allocations could have been foreseen in advance of or during, enrolment.Jutta's question mark icon.png
Study tablets were distributed primarily in calendar packs, with each blister containing three tablets: 325 mg of aspirin (or identical-appearing cellulose–sucrose placebo), 81 mg of aspirin (or placebo), and 1 mg of folic acid (or placebo). The study was double-blind: treatment assignments were not revealed to the patients or to any staff members except the statistical analyst and the pharmacy technician.
What was the risk of bias from the allocation concealment?Jutta's question mark icon.png
Describe all measures used, if any, to blind outcome assessors from knowledge of which intervention a participant received. Provide any information relating to whether the intended blinding was effective.Jutta's question mark icon.png
Among patients in the full three by-two factorial trial, a blinded analysis with further adjustment for folate-treatment assignment yielded results similar to those presented.
What was the risk of bias from the blinding of participants and personnel and outcome assessors?Jutta's question mark icon.png
Incomplete outcome data
Describe the completeness of outcome data for each main outcome, including attrition and exlusions from the analysis. State whether attrition and exclusions were reported, the numbers in each intervention group (compared with total randomized participants), reasons for attrition/exclusions where reported, and any re-inclusions in analyses performed by the review authors.Jutta's question mark icon.png
Outcome date for 1084 (those that completed a colonoscopy) out of 1121 that were randomised.
What was the risk of bias from incomplete outcome data?Jutta's question mark icon.png
Selective outcome reporting
State how the possibility of selective outcome reporting was examined by the review authors and what was found.Jutta's question mark icon.png
97% of patients included in analysis.
What was the risk of bias from selective outcome reporting? Assessments should be made for each main outcome (or class of outcomes).Jutta's question mark icon.png
Other sources of bias
Describe any other sources of biasJutta's question mark icon.png
What was the risk of bias from other sources?Jutta's question mark icon.png
Overall risk of bias
Low risk of bias Additional comments: Please replace this text and include any additional comments in regards to your risk of bias rating

Jutta's tick icon.png This appraisal has been completed.

Baron JA, Cole BF, Sandler RS, Haile RW, Ahnen D, Bresalier R, et al. A randomized trial of aspirin to prevent colorectal adenomas. N Engl J Med 2003 Mar 6;348(10):891-9 Available from:
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Topic area
Guidelines:Colorectal cancer
Clinical question
Form:Quality appraisal rct-cochrane

Section below only relevant for Cancer Council Project Officer

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