Both reliability and validity are measures of test performance, but they have separate and distinct meanings. Validity is the degree to which the data measure what they were intended to measure (i.e., accuracy) when compared with a true measure, otherwise known as a criterion standard or ‘‘gold standard.’’ The term validity is also used when referring to the ability of a test to classify subjects into dichotomous categories of diseased versus non- diseased. Reliability is the extent to which repeated measurements get similar results (i.e., precision or reproducibility). It refers to the capacity of a test to give the same result on repeated application. Reliability depends on 1) the variability in the specific manifestation on which the test is based, 2) the variability in the method of measurement, and 3) the skill with which the measurement is made. One measure of reliability, for example, would be the degree of dispersal of repeated measurements characterized as variance or standard deviation. (Kyriacou, 2001).
A diagnostic test should be both highly sensitive and highly specific. This is not usually possible as increasing sensitivity decreases specificity and vice versa. Different testing strategies have different requirements for sensitivity and specificity. Since highly sensitive tests are rarely negative in the presence of disease, these types of tests are particularly useful during the early stages of a diagnostic workup or when there is reason to suspect a dangerous illness. Highly specific tests are rarely positive in the absence of disease. Thus, these types of tests help confirm a diagnosis that is suggested by clinical data or other tests (Kyriacou, 2001).
Emphasis on HIV testing as a gateway to prevention, treatment, and care has grown tremendously over the past decade. In turn, this emphasis on testing has created a demand for new policies, programs, and technologies that can potentially increase access to and uptake of HIV testing. HIV self-testing (HST) technologies have gained important momentum following the approval of the over-the-counter self-tests in the United States, the UK, and France. While the renewed interest in HST has given rise to several high-quality reviews of empirical studies conducted on this topic, we have yet to find an article that captures the extent of the debate on HST (Gagnon, French, & Hébert, 2018). Self-tests maybe second- or third-generation HIV tests. They are only able to detect HIV antibodies, whereas the fourth-generation HIV tests which are normally used by healthcare professionals are also able to detect p24 antigen (a protein contained in HIV’s viral core that can be detected in the first few weeks after infection). Fourth-generation tests are therefore better at picking up recent infections. Second- and third-generation tests can accurately detect chronic (long-standing) HIV infection. But their ability to detect recently acquired HIV is more variable (Pebody, 2019).
Diagnostic testing has become indispensable for diagnosing and monitoring disease, for providing prognoses and for predicting treatment responses. Clearly defining the test’s purpose is important. The market should be reviewed to identify the tests available for the condition of interest by consulting guidance from international organizations such as WHO and manufacturers’ product information. Six factors to be considered when assessing whether to recommend a diagnostic test. 1. Many countries do not have regulatory procedures in place for assessing the safety, quality or effectiveness of in vitro diagnostic tests, which means that poor-quality tests can be marketed and used. 2. The performance of a test under ideal conditions (i.e. in phase-II studies) indicates its optimal performance. This information is crucial for enabling users to preselect a test for a trial under real-life conditions.3. Both the actual performance of in vitro diagnostic tests and their ease of use should also be considered during the selection process. 4. Monitoring a test’s performance in routine use is important. 5. Both the actual performance of in vitro diagnostic tests and their ease of use should also be considered during the selection process. 6. Monitoring a test’s performance in routine use is important. (Kosack, Page, & Klatser, 2017).
Reference
Gagnon, M., French, M., & Hébert, Y. (2018). The HIV self-testing debate: where do we stand?BMC Int Health Hum Rights.18(1). pp 5. doi: 10.1186/s12914-018-0146-6.
Kosack, C.S., Page, A., & Klatser, P.R. (2017). A guide to aid the selection of diagnostic tests.World Health Organization. 95. pp 639-645. doi:
http://dx.doi.org/10.2471/BLT.16.187468
KYRIACOU, D.N. (2001). Reliability and Validity of Diagnostic Tests.Academic Emergency Medicine. 8(4). pp 404-405. Retrieved from
https://onlinelibrary.wiley.com/doi/pdf/10.1111/j….
Pebody, R. (2019). How accurate is self-testing for HIV? Retrieved from
https://www.aidsmap.com/about-hiv/how-accurate-sel…