Question

5. Explain what percent agreement is, why it’s useful, and why calculations of it usually ignore agreement of negative results.

6. What is the positive predictive value of a diagnostic test? How is the PPV affected by the prevalence of the condition the test is for?
7. What is meant by the term overdiagnosis? What kind of changes have meant that it is becoming an increasing problem?

Answer 1

5.

• Percent agreement is one intercoder reliability technique that relies on the proportion of agreement of coded units between two independent judges. Percent agreement is also known as simple agreement. It is the simplest form of intercoder reliability and percent agreement is best suited for a nominal measurment level.
• Percent agreement is used in the measure of interobserver reliability in applied behavior analysis.
• Percent agreement are frequently used to represent inter examiner reliability, but it can be misleading and providing error or negative results.

6.

• Positive predictive value is the probability that subjects with a positive screening test truly have the disease. PPV can be calculated by number of true positives by number of positive calls.
• True positive is the event that the test make a positive prediction and the subject has a positive result under the gold standard.
• Prevalence will impact the positive predictive value of tests, as prevalence increases the PPV also increases, similarly when prevalence decrease the PPV decrease.

7.

• Overdiagnosis is the diagnosis of a medical condition that will never caused any symptoms ar any other problems. It can cause harmful effect, if it leads to psychological stress and unnecessary treatments.
• Screening tests can result in overdiagnosis. Overdiagnosis is a side effect of screening for early forms of disease. Even screening saves lives in some cases, it turns people into patients.
• Overdiagnosis cannot be determined during life of an individual. Increased rate of testing and disease diagnosis are the main suggestive of overdiagnosis.