Please provide solutions to the following Questions and show all necessary work.

Question

Please provide solutions to the following Questions and show all necessary work.

A colon cancer screening study is being conducted in Nottingham England. Individuals will be screened with the Hemoccult test, which has a sensitivity of 70% and specifity of 75%. Nottingham has a prevalence of 12/1000 for colon cancer. (a) What is the positive predictive value of the test? (b) What is the negative predictive value of the test? (c)] Suppose a case-control study in which 200 cases (people with colon cancer) and 200 controls (people without colon cancer) are selected from the population. All 400 people are screened with the Hemoccult test. Given the information about the test fill in the following table with the expected frequencies (d) Given the previous table what is the positive and negative predicted value of the test. Compare these numbers with your previous calculations and explainany discrepancies vou may observe Test Disease Status Total Results Present Absent a+b Positive Negative Total a+c

Explanation / Answer

Ans:

Sensitivity = the proportion of diseased people who were correctly indentified as positive by the test = TP/TP+FN=70%

Since TP+FN=12 (we getthis from the prevalence) and 70% of12 = 8.4, then TP = 8.4.

Subtract 12-8.4 toget FN= 3.6.

Specifcity = the proportion of non diseases people who are correctly identified as negative by the test = TN/TN+FP =75%.

Since FP+TN=1000-12=988.Since FP+TN= 988 (we get this from subtracting the prevalence from the total)and 75% of 988 = 751,

then TN= 751.Subtract 988-751 = 247 to get FP = 247.

Positive Predictive Value = the proportion of patients who actually have the disease that test positive

TP/TP+FP= 8.4/255.4 x 100 = 3.3%

Negative perdictive value=741/(3.6+741)=741/744.6=0.9952

Yes No Total Positive 8.4(TP) 247(FP) 255.4 Negative 3.6(FN) 741(TN) 744.6 Total 12 988 1000

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.