Practice exercise (made-up values, not clinical guidance). A town has 14 500 inhabitants. At the start of a year, 293 of them have a chronic disease. During the year, 241 more people are newly diagnosed (assume nobody moves away or dies). Find the point prevalence P at the start of the year per 1000 inhabitants. 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 accuracy Acc as a percentage. Round to one decimal place.
Practice exercise (made-up values, not clinical guidance). In a randomised trial, 220 patients received a new treatment and 360 received the control treatment. The table shows how many in each group had the outcome (an unwanted event such as a stroke). Find the number needed to treat NNT to prevent one event. Round up to a whole number of patients.
Practice exercise (made-up values, not clinical guidance). A case-control study compares 370 patients with a disease (cases) and 60 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). 10 000 people are screened with a test of sensitivity 87% and specificity 81%. The prevalence of the disease is 26%. How many true-positive results TP are expected?
Practice exercise (made-up values, not clinical guidance). A screening test has a sensitivity of 93% and a specificity of 97%. It is used in a population where the prevalence is 15%. Find the negative predictive value NPV as a percentage. Round to one decimal place.
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