Practice exercise (made-up values, not clinical guidance). A town has 33 000 inhabitants. At the start of a year, 1071 of them have a chronic disease. During the year, 144 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 sensitivity Se as a percentage. Round to one decimal place.
Practice exercise (made-up values, not clinical guidance). In a randomised trial, 890 patients received a new treatment and 810 received the control treatment. The table shows how many in each group had the outcome (an unwanted event such as a stroke). Find the absolute risk reduction ARR as a percentage. Round to one decimal place.
Practice exercise (made-up values, not clinical guidance). A test has a sensitivity of 84% and a specificity of 66%. Find the positive likelihood ratio LR+. Round to two decimal places.
Practice exercise (made-up values, not clinical guidance). A patient has a pre-test probability of 25% for a disease. A test with sensitivity 66% and specificity 80% comes back negative. Find the post-test probability p′ of the disease 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 48% in relative terms (RRR = 48%). In a patient group the risk without treatment (CER) is 37% 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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