Please answer if you know it and can answer it fully. I have posted it before an
ID: 3047771 • Letter: P
Question
Please answer if you know it and can answer it fully. I have posted it before and got incorrect answers.
1. In order to estimate counts and rates of work-related fatalities, the National Traumatic Occupational Fatality system has introduced a tick-box on the death certificate to indicate "injury at work." Kraus et al. (Am Epidemiol 1995; 141: 973-9) attempted to validate this "injury at work" classification system against a gold standard [International Classification of Diseases (ICD) death certificate codes designating deaths that occurred during work-related activities]. After reviewing a sample of 100,000 death certificates, the authors reported the following: 1,195 true positives; 788 false positives; 97,672 true negatives; 345 false negatives. ("positive" indicates that the tick-box was checked; "negative" indicates that it was not checked; "true" indicates agreement between the tick-box and the ICD code) Using the countsoedabove,complete the 2:2 table below: (2 pts)j ICD Classification Not work related Death Certificate Work-related TOTAL Work-related Not work-related TOTAL b. What are the sensitivity and specificity of the "injury at work" classification system? (4 pts) c. What is the positive predictive value? In your own words, how would you interpret this value? (3 ts Based on these data is the death certificate "injury at work" classification system likely to underestimate or overestimate the true number of work-related fatal injuries? (2 pts) d.Explanation / Answer
A)Given,
Sample size=1,00,000
True positive=1195
False positive=788
True negative=97672
False negative=345
A.a) the table would look like
ICD classification
Death certificate
Work related
Not work related
Total
Work related
1195(true positive, A)
788(false positive, B)
1983
Not work related
345(false negative, C)
97672(true negative, D)
98017
Total
1540
98460
100000
A.b) for injury at work classification system,
Sensitivity=(A/A+C)*100
Sensitivity =(1195/1195+345)*100
Sensitivity =1195/1540*100
Sensitivity =77.59%
Specificity=(D/D+B)*100
Specificity =97672/98460*100
Specificity =99.19%
A.c) positive predicted value=(A/A+B)*100
positive predicted value =1195/1983*100
positive predicted value =60.26%
This indicates that, 60.26% of deaths classified as “injury at work” are infact real/true injury at work
A.d) Positive Likelihood Ratio=sensitivity/1-specificity
Positive Likelihood Ratio =0.77/1-0.99
Positive Likelihood Ratio =77
Negative Likelihood Ratio=1-sensitivity/specificity
Negative Likelihood Ratio =1-0.77/0.99
Negative Likelihood Ratio =0.23
From the above values we can conclude that “injury at work” classification system is likely to over-estimate
ICD classification
Death certificate
Work related
Not work related
Total
Work related
1195(true positive, A)
788(false positive, B)
1983
Not work related
345(false negative, C)
97672(true negative, D)
98017
Total
1540
98460
100000