Table 1

Predefined information items which we would expect to be communicated to a person considering purchasing a test for COVID-19, and misinformation items which we would consider inappropriate to communicate, with rationale

Information item	Rationale
Who should take the test?
1. Does the website clearly explain whether it is a test for antibodies (whether you have previously had the disease) or active virus (whether you have it now)?	To help the potential purchaser select the most appropriate test type.
2. Does the website explain when to test?	Accuracy is heavily dependent on timing. Antibody tests undertaken too early have low sensitivity (they make false negative errors, that is, miss cases of COVID-19). Molecular virus tests undertaken very early or too late have reduced sensitivity.
Test accuracy information
3. Can you identify the test which is used? that is, the manufacturer	There has been significant media coverage of the accuracy of different manufacturers’ tests. Providing this information enables those interested to find out more.
4. Does the website give accuracy to detect cases? (sensitivity)	An informed potential purchaser would want to ensure tests successfully identify COVID-19.
5. Does the website give accuracy to detect non-cases? (specificity)	An informed potential purchaser would want to ensure tests did not misidentify COVID-19.
6. Does the website state how many samples the accuracy claims are based on?	Accuracy data based on few samples is less reliable. While few people may be interested in the detail of the test accuracy study design, the number of samples/patients may be of interest.
7. Does the website give information on the post-test probability of having or ruling out the disease? (Positive predictive value or negative predictive value at any prevalence)	This is the most important accuracy information for a person considering buying a test. For an individual whose molecular virus test result is positive, the positive predictive value gives them the probability that they currently have COVID-19. For an individual whose molecular virus test is negative, the negative predictive value is the probability that they do not currently have COVID-19. For an individual whose antibody test is positive, the positive predictive value is the probability that they have COVID-19 antibodies. For an individual whose antibody test is negative the negative predictive value is the probability that they do not have COVID-19 antibodies. These metrics are dependent on disease prevalence as well as sensitivity and specificity, but can reasonably be calculated with informed estimates of prevalence.
8. Does the website give a link or reference to a journal article of test accuracy?	Indicating the source of these data would help substantiate the claims, and allow interested people to find out more.
Avoiding misinformation about interpreting the test
9. Molecular virus test – does the website avoid the inaccurate statement that if you test negative you are not infectious or do not need to self-isolate?	The molecular virus tests are not very sensitive and so negative results may be false negatives, so the individual may still have the virus and be contagious.
10. Antibody test – does the website avoid the inaccurate statement that we know that test positive infers immunity or allows you to put yourself at greater risk of virus exposure?	A positive antibody test could be a false positive, meaning the individual does not have antibodies. Even if it is a true positive we do not know whether the presence of antibodies infers immunity, and how that changes over time as antibody levels drop.
Providing accurate information about interpreting the test
11. Molecular virus test – does the website state that if you test positive you should self-isolate?	Individuals who test positive on a molecular virus test are likely to have active virus, and are likely to be contagious.
12. Molecular virus test – does the website state that if you test negative you may still have the disease?	Same rationale as item 9 above, but here we assessed whether the websites gave correct information (in addition to avoiding misinformation).
13. Antibody test – does the website explain that we do not know whether a positive test infers immunity, and/or that you shouldn’t put yourself at more risk of exposure if you test positive?	Same rationale as item 10 above, but here we assessed whether the websites gave correct information (in addition to avoiding misinformation).