You are seeking to reduce morbidity and mortality caused by cancer of the oral cavity.

You are seeking to reduce morbidity and mortality caused by cancer of the oral cavity. Typically, patients are not diagnosed with oral cancer until clinical symptoms become apparent.  However, it is strongly believed that treatment will best prevent the progression of the disease if it is given before clinical symptoms appear. A new technology, a fluorescent device called OroScope, has been invented to illuminate and delineate asymptomatic early lesions of oral mucosa called leukoplakia. It can be used by individuals without specialized training. A researcher decided to pilot-test OroScope by evaluating 1,000 male smokers without any clinical signs of oral cancer. Using the OroScope, the study personnel classified 260 people as having leukoplakia. Each subject then underwent a thorough clinical evaluation by a physician specializing in oral cancers (i.e., gold standard diagnostic test). Of the 100 doctor-confirmed leukoplakias, 80 were previously identified by OroScope.

1. What is the prevalence of physician-diagnosed leukoplakia among male smokers?

P= 

2. Using the clinician evaluation as the gold standard, calculate the sensitivity, specificity PPV and NPV of OroScope in this study.

  D+ D- TOTAL

T+ 80 180 260

T- 20 720 740

  100 900 1000

Sensitivity = 

Specificity = 

PPV = 

NPV = 

After the pilot study was complete, the same team of researchers obtained additional funding to test OroScope using the same methods in a larger study (N = 10,000) for which participants were recruited from the general population.  The prevalence of physician-diagnosed leukoplakia in the general population is reported to be about 1%. 

3. What are the PPV and NPV of OroScope in the second (general population) study?  Discuss the key assumption required for your calculations.

80 1980 2060

20 7920 7940

100 9900 10000

PPV = 

NPV =

sensitivity and specificity of the test remains the same