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# Sensitivity, Specificity

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Xray No TB Yes TB Total
Negative 1739 8 1747
Positive 51 22 73
Total 1790 30 1820

Calculate the sensitivity and specificity of an X-ray as a screen for TB and write a brief conclusion statement.

https://brainmass.com/statistics/statistical-theory/sensitivity-specificity-calculations-183453

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Xray No TB Yes TB Total
Negative 1739 8 1747
Positive 51 22 73
Total 1790 30 1820

Calculate the sensitivity and specificity of an X-ray as a screen for TB and write a brief conclusion statement.
We can assume that there are four possible ...

#### Solution Summary

We can assume that there are four possible groups of patients, as indicated (a, b, c, d) in the table: ...
From these we determine the sensitivity and specificity as follows: ...

Complete, step-by-step solutions for both Sensitivity and Specificity.

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## Specificity and Predictive Value

12. Table 1. Results of a screening test for diabetes, using a cutoff point of 160 mg.dl.

True Diagnosis
Test result Diabetic Not Diabetic Total
Positive 34 20 54
Negative 116 9,830 9,946
Total 150 9,850 10,000

The specificity of the screening test for diabetes is

a. 0.3%

b. 22.6%

c. 63.0%

d. 77.4%

e. 99.7%

13. The sensitivity of the screening test for diabetes is

a. 0.3%

b. 22.6%

c. 63.0%

d. 77.4%

e. 99.7%

14. The positive predictive value of the screening test for diabetes is

a. 0.3%

b. 22.6%

c. 63.0%

d. 77.4%

e. 99.7%

15. If the cutoff is set higher than 180 mg/dl, how would this affect the sensitivity and specificity?

a. no changes

b. sensitivity increase, specificity decrease

c. sensitivity decrease, specificity increase

d. both decrease

e. both increase

16. What will be the effect on false negatives (FN) and false positives (FP) of setting the cutoff higher than 180 mg/dl?

a. FP increase, FN unchanged
b. no changes

c. FP increase, FN decrease

d. FP decrease, FN increase

e. both decrease

17. When the screening cutoff point was lowered to a blood glucose value of 130 mg/dl, 164 persons now tested positive; 98 of these people were among the 9,850 persons judged by diagnostic tests not to have diabetes. Compute the sensitivity, specificity and predictive value of a positive test at this cutoff level in the next 3 questions Sensitivity is

a. 1%

b. 40%

c. 44%

d. 56%

e. 60%

f. 99%

18. Specificity is

a. 1%

b. 40%

c. 44%

d. 56%

e. 60%

f. 99%

19. Positive predictive value is

a. 1%

b. 40%

c. 44%

d. 56%

e. 60%

f. 99%

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