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Newton et al (Gut 2001;49:282–7) described a retrospective study on bone mineral density (BMD) in a large cohort of patients with primary biliary cirrhosis (PBC). The authors concluded that osteoporosis is not a specific complication of PBC, but certain weaknesses in the study design do not support this conclusion.
The authors did not include age and sex matched controls from the general population, or control groups with different types of liver disease.
A proper methodological design comparing osteoporosis in PBC and in a normal population should calculate the standardised incidence ratio of osteoporosis for the two cohorts by comparing the observed incidence versus the expected incidence. The calculation should include 95% confidence intervals according to exact Poisson limits.1
A logistic regression analysis including risk factors for osteoporosis (that is, age, menopausal status, smoking habits, alcohol consumption, etc) should have been performed.
The major drawback however is the …