Table 1

Risk of bias assessment tool

Criteria	Response	Yes	No/not reported
A clearly stated aim	Did they have a ‘study question’ or ‘main aim’ or ‘objective’?	□	□
	The question addressed should be precise and relevant in light of available literature.	□	□
	To be scored adequate the aim of the study should be coherent with the ‘Introduction’ of the paper.	□	□
Inclusion of consecutive patients	Did the authors say: ‘consecutive patients’ or ‘all patients during period from … to….’ or ‘all patients fulfilling the inclusion criteria’?	□	□
A description of inclusion and exclusion criteria	Did the authors report the inclusion and exclusion criteria?	□	□
Inclusion of patients	Did the authors report how many eligible patients agreed to participate (ie, gave consent)?	□	□
Prospective collection of data. Data were collected according to a protocol established before the beginning of the study	Did they say ‘prospective’, ‘retrospective’ or ‘follow- up’? The study is not prospective when it is a chart review, database review, clinical guideline, or practical summaries.	□	□
Outcome measures	Did they report the association between the potential risk factors and manifestation of Achilles tendinopathy as outcome? The valid outcome measure for Achilles tendinopathy is clinical examination.	□	□
Unbiased assessment of the study outcome and potential risk factors	To be judged as adequate, the following two aspects had to be positive: Outcome and potential risk factors had to be measured independently. The outcome and potential risk factors for both cases and controls had to be assessed in the same way.	□	□
Were the determinant measures used accurate (valid and reliable)?	For studies where the determinant measures are shown to be valid and reliable, the question should be answered adequate. For studies that refer to other work that demonstrates the determinant measures are accurate, the question should be answered as adequate.	□	□
Loss to follow-up	To be judged as adequate, the following two aspects had to be positive: Did they report the losses to follow-up? Loss to follow-up was <20%.	□	□
Adequate statistical analyses	To be judged as adequate the following two aspects had to be positive: There must be a description of the relationship between the potential risk factors and Achilles tendinopathy (with information about the statistical significance). Was there adjustment for possible confounders (age, sex and body mass index) by multivariate analysis?	□	□

For each methodological criterion that is met 1 point is given. If the criterion was not met, zero points were given. Publications were considered to be of low risk of bias if: (1) a total score of at least 6 points was given and (2) 1 point was given to questions 6, 7, 8 and 10 (marked with the grey columns).