i Sensitivity o Probability(proportion of correct classification of cases Cases found /all cases 8 March 2018 16/80
8 March 2018 16/80 Sensitivity Probability (proportion) of correct classification of cases Cases found / all cases
sPecificity o Probability(proportion of correct classification of non- cases Non-cases identified /all non-cases 8 March 2018 17/80
8 March 2018 17/80 Specificity Probability (proportion) of correct classification of noncases Non-cases identified / all non-cases
True Disease status Cases Non-cases Positive rue False Screening Test positive positive a+ b ab Results Negative False True negative negative c+ a tc b+d T rue positives a Sensitivity All cases a+c True negatives S p ecific Ity All non-cases b+d 8 March 2018 18/80
8 March 2018 18/80 True positive True negative False positive False negative a + c b + d Sensitivity = True positives All cases = a a + c a + b c + d True Disease Status Cases Non-cases Positive Negative Screening Test Results a d b c Specificity = True negatives All non-cases = d b + d
True Disease status Cases Non-cases 140 1,0001.140 Screening Positive a Test cd Results Negative 60 19.00019060 200 20.000 Sensitivity True positives 140 70% All cases 200 S True negatives_ 19,000 pecificity 95 All non-cases 20.000 8 March 2018 1980
8 March 2018 19/80 True Disease Status Cases Non-cases Positive Negative Screening Test Results a d 1,000 b c 60 Sensitivity = True positives All cases 200 20,000 = Specificity = True negatives All non-cases = 1,140 19,060 140 19,000 140 200 19,000 20,000 = = 70% 95%
nterpreting test results predictive value o Probability(proportion of those tested who are correctly classified positive predictive value, (PPV) Cases identified/all positive tests negative predictive value, (NPV) Non-cases identified /all negative tests 8 March 2018 20/80
8 March 2018 20/80 Interpreting test results: predictive value Probability (proportion) of those tested who are correctly classified positive predictive value, (PPV) Cases identified / all positive tests negative predictive value,(NPV) Non-cases identified / all negative tests