Table 1 Level of evidence (GRADE) adapted from Guatt et al. [36] and Horvath [37]

Further research is very unlikely to change our confidence in the estimate of effect;

Very good quality of the results (validity and reliability measures > 0.8);

Well described sample selection;

Large sample size (n > 100 /for each group) or very good representativeness of the population that was intended to be sampled

Confirmatory data analysis and relevant statistical test(s)

Large magnitude effect;

Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate;

Good quality of the results (validity and reliability measures > 0.6);

Adequate sample size (n = 30–100 / for each group) or good representativeness of the population that was intended to be sampled;

Further research is very likely to change our confidence in the estimate of effect;

Moderate quality of the results (validity and reliability measures > 0.4);

Small sample size (n < 30 / for each group) or weak representativeness of the population that was intended to be sampled

Wide confidence intervals for estimates of test accuracy, or true and false positive/negative rates;

Unexplained inconsistency in sensitivity, specificity or likelihood ratios;

Any estimate of effect is very uncertain;

Evidence from expert committee report or experts;

Sample size or selection not described;

Wide confidence intervals for estimates of test accuracy, or true and false positive/negative rates;

Unexplained inconsistency in sensitivity, specificity or likelihood ratios;