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Association between competing interests and authors' conclusions: epidemiological study of randomised clinical trials published in the BMJ

BMJ 2002; 325 doi: https://doi.org/10.1136/bmj.325.7358.249 (Published 03 August 2002) Cite this as: BMJ 2002;325:249

Two types of correlation.

Kjaergard and Als-Nielsen [ ref 1] refer in their paper to the
‘interclass correlation co-efficient’ as a measure of agreement between
two raters on a continuous scale. This is
probably a mistake. I suspect they mean to refer to the intraclass
correlation coefficient, which is a standard and widely used measure of
agreement.

I had never previously heard of the interclass correlation co-
efficient. It is not a term that is widely used but I did discover that it
was used by R. A. Fisher as a label for the standard form of correlation
(Pearson product-moment correlation) to distinguish it from intraclass
correlation in one of his classic statistical textbooks. [ref 2]

1 Kjaergard L L and Als-Nielsen B. Association between competing
interests and authors’ conclusions: epidemiological study of randomised
clinical trials reported in the BMJ. BMJ 2002; 325: 249 (3 August)

2 Fisher R A. Statistical Methods for Research Workers. Edinburgh:
Oliver and Boyd, 1925

Competing interests: No competing interests

06 August 2002
William P Plummer
Consultant Psychiatrist
East Kent community NHS Trust, Canterbury, Kent. CT1 1AZ