A key step for systematic review preparation includes an evaluation of the reliability of clinical trials.
Clinical trials are either part of experimental or observational studies, with each type of study evaluated from a different perspective. This requires us to use a different scale/questionnaire for each study design evaluation:
- Jadad scale for experimental studies with random assignment of patients to treatment arms;
- Tool from Cochrane Handbook for Systematic Reviews of Interventions to assess risk of bias in RCT, taking into account: proper patient selection, latency randomisation code, blinding or loss of observed patients (assessment in tabular and graphical form);
- Newcastle – Ottawa Quality Assessment Scale for observational studies with a control group;
- NICE 2003 Scale for assessing credibility of uncontrolled studies (case series);
- The modified Effective Public Health Practice Project Quality Assessment Tool (EPHPP) – the universal scale evaluating different types of studies.
To assess whether the evaluation meets criteria required for the systematic review, we use the most popular tool called the Cook criteria, which analyses the following criteria:
- Clinical precision of the question;
- Timeliness and sensitivity of the search strategy used and its presentation; and
- Presence of pre-defined criteria for inclusion and exclusion of studies and assessment of their credibility.
The systematic review is evaluated in terms of statistical method accuracy and the reasonableness of quantitative synthesis of the results (performance of meta-analysis). Subsequently, the validity of conducted inferences is assessed in the context of possible restrictions of the review.
In addition, we also use the following checklists to assess the resulting systematic review: PRISMA (Reporting Items for Systematic Reviews and Meta-Analyses) and AMSTAR (A Measurement Tool to Assess Systematic Reviews and Meta-analysis).