Table 4.
| Modified QUADAS item (Topic/Bias) | Interpretation |
|---|---|
| 5. Did the whole sample or a random selection of the sample receive verification using a reference standard of diagnosis? (Partial verification bias) | This item concerns partial verification bias, which is a form of selection bias that occurs when not all of the study participants receive the reference standard (in our context, confirmation of the TRUE disease status of the relative). Sometimes the reason only part of the sample receives the reference standard is that knowledge of the index test results influence the decision to perform the reference standard. Note that in the context of family history, the reference standard can only be applied to family members or relatives. The self report by the probands or informants is the “index test” |
| We consider the whole sample to be ALL relatives for which the proband or informant provided information (including “don’t know” status) | |
| YES: All relatives that the proband identifies/ reports upon represent the whole sample of relatives. As such, some form of verification is attempted for all identified relatives | |
| NO: Not all relatives receive verification via the reference standard. As such, we consider partial verification bias to be present in the following situations: | |
| 1) Knowledge of the index test will determine which relatives are reported to have the disease status. Often UNAFFECTED relatives do not have their disease status verified by any method (assume proband/informant report is the true disease status); in this case, the disease status is verified in the AFFECTED relatives only. In this situation, the outcomes of sensitivity and specificity cannot be computed | |
| 2) Relatives for which the proband/ informant indicates “don’t know status” are excluded and do not have their disease status verified (no reference standard testing) | |
| 3) Relatives who are DECEASED are excluded from having any verification undertaken (no reference standard testing) | |
| 4) Relatives who are UNABLE TO PARTICIPATE in interviews or further clinical testing are excluded from having any verification method (no reference standard testing) | |
| UNCLEAR: Insufficient information to determine whether partial verification was present |
* See text
Abbreviation: QUADAS = Quality Assessment of Diagnostic Accuracy Studies