The authors of a study wanted to assess the accuracy of a questionnaire used to
ID: 3449370 • Letter: T
Question
The authors of a study wanted to assess the accuracy of a questionnaire used to diagnose depression. They selected a random set of elderly residents living at an assisted facility and assessed medical records to determine who did and did not have depression, which had been assessed upon arrival at the facility and regularly thereafter. This assessment served as a “gold standard” for the analysis. The table below shows the data from the subgroup analysis.
Results of the depression questionnaire
Depression
(Medical record)
No Depression
(Medical record)
TOTAL
Depression (Questionnaire)
52
112
164
No Depression
(Questionnaire)
8
74
82
TOTAL
60
186
246
Calculate the sensitivity of the screening test.
Calculate the specificity of the screening test.
Calculate the positive predictive value of the screening test.
Calculate the negative predictive value of the screening test.
Results of the depression questionnaire
Depression
(Medical record)
No Depression
(Medical record)
TOTAL
Depression (Questionnaire)
52
112
164
No Depression
(Questionnaire)
8
74
82
TOTAL
60
186
246
Explanation / Answer
The sensitivity detects 2/3rd of people with diease, it misses out 1/3rd. 52/ (52+8) *100 = 86.6% Hence 86% amonst 60 have depression
Specificity = D/(D+B)*100 = 39.7% hence 39.7% ammongst 186 have no depression
Positive predictive value = 52/ (52+112)*100 = 31.7%. Hence people who are tested positive are only 31.7%
Negative predictive value = 74 / (74+8) * 100 = 90.2%. And those who are tested negative are 90.2%
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