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 town has 8500 inhabitants. At the start of a year, 131 of them have a chronic disease. During the year, 46 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). In a cohort study, exposed people contributed 5700 person-years with 684 new cases, and unexposed people 7900 person-years with 237 new cases. Find the incidence rate ratio IRR (exposed versus unexposed). Round to two decimal places.
Practice exercise (made-up values, not clinical guidance). In a randomised trial, 580 patients received a new treatment and 230 received the control treatment. The table shows how many in each group had the outcome (an unwanted event such as a stroke). Find the relative risk RR of the event with treatment. Round to two decimal places.
Practice exercise (made-up values, not clinical guidance). A screening test has a sensitivity of 93% and a specificity of 99%. It is used in a population where the prevalence is 5%. 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 45% in relative terms (RRR = 45%). In a patient group the risk without treatment (CER) is 34% 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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