Evidence-based practice statistics worksheet with answers

Practice exercise (made-up values, not clinical guidance). A town has 5500 inhabitants. At the start of a year, 158 of them have a chronic disease. During the year, 83 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). 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). A case-control study compares 190 patients with a disease (cases) and 550 people without it (controls). The table shows how many in each group were exposed to a risk factor. Find the odds ratio OR for the exposure. Round to two decimal places.

Practice exercise (made-up values, not clinical guidance). A test has a sensitivity of 64% and a specificity of 79%. Find the positive likelihood ratio LR+. Round to two decimal places.

Practice exercise (made-up values, not clinical guidance). 10 000 people are screened with a test of sensitivity 99% and specificity 97%. The prevalence of the disease is 8%. How many people with the disease are missed by the test (false negatives, FN)?

Practice exercise (made-up values, not clinical guidance). A treatment reduces the risk of an event by 21% in relative terms (RRR = 21%). In a patient group the risk without treatment (CER) is 11% 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.