Table 1 Criteria of high, moderate and low study quality, mainly according to QUADAS[21]

High: small risk of bias

Prospective study design. Particular emphasis on the following:

● adequately described patients constituting a representative and clinically relevant sample (QUADAS items 1, 2).

● the index test should not form part of the reference standard (item 7).

● evaluators should be masked to results of index test and reference test (items 10, 11)

● the tests should be described in sufficient detail to permit replication (items 8, 9).

● sample size ≥ 5000.

● diagnostic accuracy presented as sensitivity and specificity.

Moderate: moderate risk of bias

Prospective study design

Since no prospective studies based on digital mammography could be identified, scanned analogue images were accepted. Otherwise the same criteria as for high quality were required.

Low: high risk of selection and/or verification bias

Retrospective study design. Selected or enriched samples