Question

A medical research team identified a new peptide growth factor, breast carcinoma promoting factor (BCPF) in explant cultures of breast tumors. A pilot study revealed that plasma levels of BCPF were elevated in confirmed breast cancer patients. The investigators conducted a clinical trial to determine criterion of 150 units /L. The investigators found out that the BCPF had a sensitivity of 95% and specificity of 85%. A health researcher now wishes to assess the predictive ability of the BCPF test in a population in which the prevalence of breast cancer is 5%. The researcher working with the three hospitals in the city was able to recruit 1600 women for the study.

1.1. Develop a two-by-two table using the above information. Label the columns and rows properly. Provide the marginal totals. Show all calculations. 1.2. What is the positive predictive value of BCPF in this study population? Interpret it. 1.3. What is the negative predictive value of BCPF in this study population? Explain your finding.

Answer 1

1.1

Sensitivity: The probability of a person testing positive, given that (s)he has the disease.

Specificity: The probability of a person testing negative given that (s)he does not have the disease.

Let D shows the event that person has disease and P shows the event that person gives positive results and N shows the event that person has negative results.

Following is the completed table:

		Test Result
		Positive(P)	Negative(N)	Total
	Yes, D	0.95*0.05=0.0475	0.05-0.0475=0.0025	0.05
Cancer	No	0.95-0.8075=0.1425	0.85*0.95=0.8075	1-0.05=0.95
	Total	0.19	0.81	1

1.2:

Positive predictive value is the probability that person has disease given that test gives positive result so

Negative predictive value is the probability that person has no disease given that test gives negative result so