Another Investigator Independently Performed Epid
Screening:
Calculate and interpret sensitivity, specificity, positive predictive value of screening tests.
1. A study was conducted in a medical school hospital to evaluate whether visual inspection of the cervix (by speculum examination) would be a useful screening test for cervical Logistically, pap smears are not always possible to perform in the field and a simple visual inspection test, if found valid and reliable, could be a life saving procedure in such settings.
660 consecutive patients with suspected cervical cancer who attended an obstetrics and gynecology out-patient clinic were admitted to a referral hospital. A trained nurse performed visual inspection of the cervix on all of these patients and classified the results as positive or negative. Subsequently, another investigator independently performed cervical biopsy (gold standard) on all of the patients. The investigators were blinded to each other’s findings. 330 of the 660 patients had cervical cancer on histopathological (biopsy) examination. The results [fictitious data] are shown in Table 6 below:
- Calculate the following test properties and interpret
(a) Sensitivity:
(b) Specificity:
(c) Positive predictive value [PPV]:
(d) Negative predictive value [NPV]:
(e) Based on the above results, how useful do you think the visual inspection test is for diagnosing cancer of the cervix?
2. If this test had been performed in a primary care setting (instead of a medical school hospital) with a baseline cervical cancer prevalence of 10%, what would have been the test performance? For this, you need to use the same sensitivity and specificity values obtained in the study, but apply these to a different population with 10% prevalence of Use the blank table given below (Table 7). Assume that the same numbers of patients are being screened (660). Hint: you will have 66 total positives based on histopathology
- Calculate the following test properties and interpret.
(a) Positive predictive value:
(b) Negative predictive value:
- From the above information, complete the below table:
(a) From this table, what can you infer?