Intraclass correlation coefficientBMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f1816 (Published 22 March 2013) Cite this as: BMJ 2013;346:f1816
- Philip Sedgwick, reader in medical statistics and medical education
- 1Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
Researchers investigated the association between bone mineral density measurements in twins, with monozygotic (identical) and dizygotic (non-identical) twins studied separately. The comparison was part of a study that investigated the association between vitamin D receptor genotype and bone mineral density in postmenopausal twins. A cross sectional study design was used, with participants recruited from a national register of twins in Britain. Participants were 87 monozygotic and 95 dizygotic pairs of twins aged 50-69 years, postmenopausal, and free of diseases affecting bone.1
The main outcome measures included lumbar spine bone mineral density as measured by dual energy x ray absorptiometry. The intraclass correlation coefficient for lumbar spine bone mineral density between monozygotic twins was higher than for dizygotic ones (0.74 v 0.36). It was concluded that in British postmenopausal women’s lumbar spine bone mineral density was genetically linked.
Which of the following statements, if any, are true?
a) The intraclass correlation coefficient provided a measure of agreement between measurements of lumbar spine bone mineral density for sets of twins
b) The intraclass correlation coefficient can take a value from −1 through 0 to +1
c) Agreement between lumbar spine bone mineral density measurements was greater for monozygotic twins than for dizygotic ones
Statements a and c are …