Practice exercise (made-up values, not clinical guidance). A town has 47 500 inhabitants. At the start of a year, 1202 of them have a chronic disease. During the year, 433 more people are newly diagnosed (assume nobody moves away or dies). Find the cumulative incidence CI over the year per 1000 people at risk. Round to one decimal place.
Practice exercise (made-up values, not clinical guidance). A new test was compared with the reference standard in a study (see the 2 × 2 table). Find the specificity Sp as a percentage. Round to one decimal place.
Practice exercise (made-up values, not clinical guidance). A case-control study compares 110 patients with a disease (cases) and 790 people without it (controls). The table shows how many in each group were exposed to a risk factor. Find the odds ratio OR for the exposure. Round to two decimal places.
Practice exercise (made-up values, not clinical guidance). A new test was compared with the reference standard in a study (see the 2 × 2 table). Find the negative likelihood ratio LR−. Round to two decimal places.
Practice exercise (made-up values, not clinical guidance). A screening test has a sensitivity of 73% and a specificity of 82%. It is used in a population where the prevalence is 1%. Find the positive predictive value PPV as a percentage. Round to one decimal place.
Practice exercise (made-up values, not clinical guidance). A treatment reduces the risk of an event by 50% in relative terms (RRR = 50%). In a patient group the risk without treatment (CER) is 4% over five years. Find the number needed to treat NNT for five years to prevent one event. Round up to a whole number of patients.
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