Critical appraisal:Logan RF, Grainge MJ, Shepherd VC, Armitage NC, Muir KR, ukCAP Trial Group 2008

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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
Randomization to treatment group was performed centrally (Queen’s Medical Centre, Nottingham, UK). Patients were randomized to 1 of 4 treatment arms based on the 2 � 2 factorial design using a computergenerated randomization list with a block size of 8, with randomization stratified by center. The randomization schedule for each center was made available to regional pharmacists.
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
The researchers and all clinical staff involved with patient recruitment were blind to this treatment-allocation schedule.
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
Study participants, clinical staff involved with patient surveillance, and investigators at the coordinating center in Nottingham were all blinded to treatment. Only trial pharmacists had knowledge of the treatment administered.
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
A total of 853 patients underwent a follow-up endoscopic examination (90.8% of those randomized). Reasons for a follow-up examination not being performed included death, poor health, and failure to contact patients who previously had withdrawn from taking study medication (Figure 1). Of the patients who had a second colonoscopy, 144 (16.9%) had withdrawn from taking both study medications by the time of their follow-up examination (Figure 1). An additional 81 patients withdrew from the aspirin arm of the study only, the most common reason being that the patient had a clinical indication for either aspirin or a medication that potentially could contraindicate aspirin treatment (n � 53). The number of patients withdrawing from the aspirin

arm of the trial was slightly higher among those who were assigned to aspirin than assigned to placebo aspirin
treatment (49 vs 32 patients). Only 1 patient withdrew from the folate arm of the trial only.

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
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

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Logan RF, Grainge MJ, Shepherd VC, Armitage NC, Muir KR, ukCAP Trial Group. Aspirin and folic acid for the prevention of recurrent colorectal adenomas. Gastroenterology 2008 Jan;134(1):29-38 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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