4.1 - 4.6 See pp. 95 - 96 in the text.
4.7 Cross-tabulated diagnostic results from two independent
raters are:
|
Rater B |
|
|
Rater A |
+ |
- |
Total |
+ |
150 |
31 |
181 |
- |
28 |
239 |
267 |
Total |
178 |
270 |
448 |
Calculate the kappa statistic for these results.
Interpret this finding. [You may check your calculations
with the “Screening Calculator” under the “Counts”
folder in http://www.openepi.com.]
4.8 Calculate this test's sensitivity and specificity.
|
Gold Standard |
|
|
Test |
+ |
- |
Total |
+ |
15 |
7 |
22 |
- |
3 |
145 |
148 |
Total |
18 |
152 |
170 |
4.9 Why is exercise 4.7 a reproducibility analysis? Why is exercise 4.8 a validity analysis?
4.10 Predicting tornadoes, kappa. During four months in 1884, J. P. Finley predicted
whether or not one or more tornadoes would occur in each of eighteen areas of
the
|
Actual occurrence |
|
|
Prediction |
+ |
- |
Total |
+ |
11 |
14 |
25 |
- |
3 |
906 |
909 |
Total |
14 |
920 |
934 |
4.11 Predicting tornadoes,
predictive value positive. Calculate
the predictive value positive of Finley’s predictions using the data in exercise
4.10. How did Finley do? [Consider the finding in this question and the
findings in question 4.10.]
4.12
Screening for bladder cancer. A screening test for bladder cancer uses the staining
properties of exfoliated cells in the urine to detect potential bladder cancer
cases. Two pathologists review 500
samples and come up with the following diagnoses:
|
Pathologist
B |
|
|
Pathologist A |
+ |
- |
Total |
+ |
9 |
2 |
11 |
- |
0 |
489 |
489 |
Total |
9 |
491 |
500 |
a. Explain why this is a
reproducibility analysis, and not a validity analysis.
b. Assess the reproducibility of
these results.
c. Further development of the test
proves it to have a sensitivity of 90% and specificity of 98%. This test is
used in 100,000 individuals from a population in which the prevalence of
subclinical bladder cancer is 0.1% (i.e., 0.001). Set up a 2-by-2
table showing the number of true positives, true negatives, false positives,
and false negatives expected when using this screening test in this
population.
d. What is the predictive value of a
positive test in this population?
e. What is the predictive value or a
negative test in this population?
f. The same test is used in a
patient population demonstrating chronic hematuria
and other symptoms of possible bladder cancer. The prevalence of bladder cancer
in this clinical population is 1 in 10. Set up a 2-by-2 table showing the
distribution of true positives, true negatives, false positives, and false
negatives expected when using the test in 1000 people from this clinical
population.
g. What is the predictive value of a
positive test when used in the clinical population described in item f?
h. Why is the
predictive
value positive of the test in the clinical population so much greater than in
the general population?
4.13 Updating the Case Study in the text. The case study that begins on p. 98 in the text
provides a way to acquaint yourself with strengths and
limitations of population-based screening procedures. It is, however, out of
date in terms of sensitivity and specificity specifications. We might consider
redoing this case study assuming the EIA screening kit described on p. 99 has a
sensitivity of 98% and its specificity is 98.83% – see http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0008217#top
for current estimates of specificty. Also, now assume Western Blot (WB) test considered
on page 101 has a sensitivity of 97% (.97) and specificity of 99.99%
(.9999).
4.14 Interexaminer Reliability Of A Leg Length Analysis (Holt et al., 2009). A study to evaluate the interexaminer reliability of a leg length analysis protocolbetween an experienced chiropractor and an inexperienced chiropractic student who has undergone an intensive training program found these data for examination in the supine extended leg position:
|
Rater B |
|
|
Rater A |
+ |
- |
Total |
+ |
12 |
2 |
14 |
- |
4 |
28 |
32 |
Total |
16 |
30 |
46 |
a. Calculate the percent agreement between the raters.
b. Calculate the kappa statistic and interpret this result.