Practice exercise (made-up values, not clinical guidance). A town has 20 500 inhabitants. At the start of a year, 160 of them have a chronic disease. During the year, 194 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 town has 13 500 inhabitants. At the start of a year, 190 of them have a chronic disease. During the year, 54 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 test has a sensitivity of 62% and a specificity of 89%. Find the negative likelihood ratio LR−. Round to two decimal places.
Practice exercise (made-up values, not clinical guidance). In a cohort study, exposed people contributed 7000 person-years with 378 new cases, and unexposed people 4700 person-years with 127 new cases. Find the incidence rate ratio IRR (exposed versus unexposed). Round to two decimal places.
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 25% 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). Without a drug, 7% of patients have a certain side effect during a year. The drug raises this risk with a relative risk of RR = 1.81. Find the number needed to harm NNH: how many patients must take the drug for a year for one extra patient to have the side effect? Round up to a whole number of patients.
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