Question

For Questions 22 through 24, please refer to the following scenario. A new screening test for Lyme disease is developed for use in the general population. The sensitivity and specificity of the new test are 60% and 70%, respectively. Three hundred patients are screened at a clinic during the first year the new test is implemented. The prevalence of Lyme disease among clinic patients is 10%. Gold Standard diagnosis Disease Yes Disease No Total ScreeningPositive Negative 22. (3 points) Fill in the 2 X 2 table to describe the patients who were screened positive/negative and do/do not have the disease based on your knowledge of the prevalence of Lyme disease. 23. (2 points) Calculate and explain the positive predictive value of the screening test. 24. (2 points) Calculate and explain the negative predictive value of the screening test

Answer 1

22Q/A	Screening	Disease YES	Disease NO	Total
	Positive	18	81	99
	Negative	12	189	201
		30	270	300

Prevalence rate of Lyme Disease is = 10%

Total patients screened is =300

So that Lyme disease screening confirmed with disease YES is = 300*10/100 = 30 patients

Lyme disease screening confirmed with disease NO is = 300-30 =270 patients

sensitivity of the new test is = 60%

so that out of 30 patients screening positive disease YES is = 30*60/100 = 18 patients(True Positive)

out of 30 patients screening negative disease YES is = 30-18 = 12 patients(False negative)

specificity of new test is =70%

so that out of 270 patients screening negative disease NO is = 270*70/100 = 189 patients (True negative)

out of 270 patients screening positive disease NO is = 270-189 = 81 patients (False positive)

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23Q/A .positive predictive value of screening test = patient with disease with positive screen/Total patients who screened

   = 18 + 81/300 = 99/300 = 0.33

24 Q/A Negative predictive value of screening test = patient without disease with negative screen/Total patients who screened    = 189 + 12/300    = 201/300    = 0.67