Critical appraisal:Rothwell PM, Wilson M, Elwin CE, Norrving B, Algra A, Warlow CP, et al 2010 1

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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
Eligible patients were allocated treatment with aspirin or placebo according to a prescribed randomisation arrangement generated separately for each clinical centre. Each patient received a randomisation code number, according to which the local pharmacy supplied the study drug. A special drug packaging and shipment procedure was used to maintain blindness of the treatment code. A sealed envelope, with information on the treatment allocated, was kept in the clinical file of each patient. In an emergency, the seal could be broken and the treatment code disclosed, at the discretion of the case physician.
What was the risk of bias from the random sequence generation?Jutta's question mark icon.png
Low
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
Each patient received a randomisation code number, according to which the local pharmacy supplied the study drug. A special drug packaging and shipment procedure was used to maintain blindness of the treatment code.
What was the risk of bias from the allocation concealment?Jutta's question mark icon.png
Low
Blinding
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
Aspirin was supplied as 75 mg, film-coated tablets in strip charts, each package containing 140 tablets; the placebo tablets were identical in appearance and packaging.


A special drug packaging and shipment procedure was used to maintain blindness of the treatment code. A sealed envelope, with information on the treatment allocated, was kept in the clinical file of each patient. In an emergency, the seal could be broken and the treatment code disclosed, at the discretion of the case physician.

What was the risk of bias from the blinding of participants and personnel and outcome assessors?Jutta's question mark icon.png
Low
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
For long-term follow-up of each trial cohort, colorectal cancers were identified (blind to treatment allocation) from death certificate and cancer registration data—coded according to the 9th or 10th revision of the International Classification of Diseases.12 Data on death due to colorectal cancer (defined as those in which the cancer had been recorded as the primary underlying cause of death on the death certificate) were available from all trials. Data set seems complete with intention-to-treat analysis.
What was the risk of bias from incomplete outcome data?Jutta's question mark icon.png
Low
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
We studied trials of aspirin versus control in the UK or Sweden in the 1980s and early 1990s, because these two countries had centralised death certifi cation established by the 1980s (and cancer registration in the UK) making these data available for research. Eligible trials had to have recruited at least 1000 participants and to have a median scheduled treatment period of at least 2·5 years (since the eff ect of aspirin on risk of colorectal cancer increased with treatment duration at the high doses).12 Five trials fulfi lled these criteria,23,24,26,27,33 but records of one had been destroyed (Juul-Moller S, University Hospital, Malmo, Sweden, personal communication). We therefore followed up four randomised trials of aspirin versus control in primary (Thrombosis Prevention Trial [TPT],23 British Doctors Aspirin Trial [BDAT]27) and secondary (Swedish Aspirin Low Dose Trial [SALT],24 UKTIA Aspirin Trial [UK-TIA]26) prevention of vascular. Long term follow-up data on cause of death were also available from the Dutch TIA trial.25
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
Low
Other sources of bias
Describe any other sources of biasJutta's question mark icon.png
None to report.
What was the risk of bias from other sources?Jutta's question mark icon.png
Low
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.


Article
Rothwell PM, Wilson M, Elwin CE, Norrving B, Algra A, Warlow CP, et al. Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials. Lancet 2010 Nov 20;376(9754):1741-50 Available from: http://www.ncbi.nlm.nih.gov/pubmed/20970847.
Assigned to
User:Albert.chetcuti
Topic area
Guidelines:Colorectal cancer/Primary Prevention
Clinical question
Form
Form:Quality appraisal rct-cochrane
Outcomes
CRC mortality
Clinical trial
Clinical_trial:SALT_Trial
Notes
Critically appraise the long term follow up for the SALT-Trial. Original trial data publication http://wiki.cancer.org.au/australia/Citation:Norrving_B,_Elwin_CE,_Peterson_B,_Blomstrand_C,_Olsson_JE,_Nilsson_B,_et_al1991

Section below only relevant for Cancer Council Project Officer

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