Practice exercise (made-up values, not clinical guidance). A town has 18 000 inhabitants. At the start of a year, 406 of them have a chronic disease. During the year, 121 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 positive predictive value PPV as a percentage. Round to one decimal place.
Practice exercise (made-up values, not clinical guidance). In a randomised trial, 570 patients received a new treatment and 300 received the control treatment. The table shows how many in each group had a side effect. Find the relative risk RR of the event with treatment. Round to two decimal places.
Practice exercise (made-up values, not clinical guidance). In a randomised trial, 810 patients received a new treatment and 330 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 treatment reduces the risk of an event by 45% in relative terms (RRR = 45%). In a patient group the risk without treatment (CER) is 5% 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.
Practice exercise (made-up values, not clinical guidance). A screening test has a sensitivity of 83% and a specificity of 84%. It is used in a population where the prevalence is 10%. Find the negative predictive value NPV as a percentage. Round to one decimal place.
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