Evidence-based practice statistics worksheet with answers

Practice exercise (made-up values, not clinical guidance). A town has 32 000 inhabitants. At the start of a year, 925 of them have a chronic disease. During the year, 137 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 36 000 inhabitants. At the start of a year, 611 of them have a chronic disease. During the year, 359 more people are newly diagnosed (assume nobody moves away or dies). Find the cumulative incidence CI over the year per 1000 people at risk. Round to one decimal place.

Practice exercise (made-up values, not clinical guidance). In a cohort study, exposed people contributed 5500 person-years with 182 new cases, and unexposed people 5300 person-years with 117 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 cohort, groups of people were followed for different lengths of time (see the table: number of people and years of follow-up for each). During follow-up, 18 new cases occurred. Find the incidence rate IR per 1000 person-years. Round to one decimal place.

Practice exercise (made-up values, not clinical guidance). A treatment reduces the risk of an event by 25% in relative terms (RRR = 25%). In a patient group the risk without treatment (CER) is 15% 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, 4% of patients have a certain side effect during a year. The drug raises this risk with a relative risk of RR = 2.3. 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.