Diagnosis Examination(MMSE) in detecting dementia among elderly patients living in the community. Excel

Sensitivity The proportion of individuals with the disease who are correctly diagnosed by the test. Example: 27 out of 39 cases were identified positive on the MMSE. that is, 69% of people with dementia will test positive on the MMSE.

Specificity The proportion of individuals without the disease who are correctly identified by a diagnostic test Example: 209 out of 335 non-cases were identified negative on the MMSE. that is, 89% of people without dementia will test negative on MMSE. Sensitivity and specificity are properties of the instrument.

Positive predictive value The proportion of individuals with a positive test result who have the disease. Example: 27 out of 53 positive results have dementia. that is, 51% of those scoring positive on the MMSE will actually have dementia.

Negative predictive value The proportion of individuals with a negative test result who do not the disease. Example: 209 out of 221 negative results do not have dementia. that is, 95% of those scoring negative on the MMSE will actually not have dementia. Unfortunately, PPV and NPV are dependent on the prevalence of the disease. Excel

Positive Likelihood Ratio LR+ The likelihood ratio of a positive test result (LR+) is the likelihood that a positive test result comes from a person with the disease rather than one without. that is, a positive result on the MMSE is 6.3 times more likely to be found in a patient with dementia rather than one without.

Negative Likelihood Ratio LR- The likelihood ratio of a negative test result (LR-) is the likelihood that a negative test result comes from a person without the disease rather than one with. that is, a negative result on the MMSE is 0.35 times more likely or 3 times less likely to be found in a patient with dementia rather than one without.

Probability and Odds Probability statements are quantified on a scale ranging from 0 to 1. 1 Impossible Certain An event with probability 1/5 or 0.2 means that there is a 1 in 5 chance of it is happening. But odds against the event are 4 to 1 and in favour 1 to 4.

Pre-test-odds that is, any patient is about a one sixth as likely to have dementia as not. The pre-test-probability is the same the prevalence rate: 39/274 = 0.14

Post-test-odds Post test odd (of positive result) = Pre test odds x LR+ Post test odds = 0.16 x 6.3 = 1 that is, a patient scoring positive on the MMSE is the same to have dementia than not.