The Critical thinking and Appraisal Resource library (CARL) to understand and assess treatment claims

Every day, we are confronted by claims about effects of treatments, many of which are not supported by evidence and are misleading. It is easy to overestimate the benefits of treatments and to underestimate their potential risks, without knowing how to accurately assess claims about treatments.

To address these problems, Castle and colleagues developed the Critical thinking and Appraisal Resource library (CARL) as a resource to help people think critically about the treatment claims they encounter. CARL is a database of learning resources organised around key concepts necessary to assess how trustworthy a treatment claim is. Specifically, the concepts address whether:

  • a claim is reliable; i.e. whether it is based on fair comparisons of treatments
  • the results of fair comparisons are relevant to the reader
  • additional information is needed to assess the reliability and relevance of claims about treatments

The learning resources in CARL are organised around these key concepts on claims, comparisons and choices – these concepts are needed to judge the trustworthiness of treatment claims. Over 300 open access learning resources were made available online by the James Lind Initiative in Testing Treatments interactive (TTi) English. CARL was designed to target ‘intermediaries’ of knowledge, e.g. teachers of schoolchildren, undergraduates and graduates, those teaching evidence-based medicine, or those communicating treatment claims to the public. Consequently, learning resources can also be filtered by resource type (e.g. websites, texts, cartoons, videos), target audience (e.g. schools, researcers, self-directed learning), and language.

Users are invited to peruse the learning resources on CARL to better understand how to appraise treatment claims.


Castle JC, Chalmers I, Atkinson P, Badenoch D, Oxman AD, et al. (2017) Establishing a library of resources to help people understand key concepts in assessing treatment claims—The “Critical thinking and Appraisal Resource Library” (CARL). PLOS ONE 12(7): e0178666.


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