13. A researcher is interested in studying the differences between a novel test for influenza and the current gold standard of a nasal swab. The researcher collects data from 1,843 patients over a period of 6 months. Which of the following statements concerning positive predictive value (PPV) is correct? A. PPV is the proportion of tests that are true positives; if disease prevalence is low, then PPV will be low. B. PPV is the proportion of tests that are true positives; if disease prevalence is high, then PPV will be low. C. PPV is the proportion of tests that are true positives; disease prevalence has no effect on PPV. D. PPV is the proportion of tests that are false positives; if disease prevalence is low, then PPV will be low. E. PPV is the proportion of tests that are false positives; if disease prevalence is high then PPV will be low