Correction
==========


In the third instalment of our series about evidence-based medicine,1 the source of the qualitative classification of kappa shown in Table 1 was incorrectly cited. The correct reference is Sackett DL, Haynes RB, Guyatt GH, Tugwell P. *Clinical epidemiology: a basic science for clinical medicine*. 2nd ed. Boston: Little, Brown and Co; 1991. p. 30.

## Reference

1.  1. McGinn T, Wyer PC, Newman TB, Keitz S, Leipzig R, Guyatt G, for Evidence-Based Medicine Teaching Tips Working Group. Tips for teachers of evidence-based medicine: 3. Understanding and calculating kappa. *CMAJ* 2004;171(11):Online-1 to Online-9. Available: [www.cmaj.ca/cgi/data/171/11/1369/DC1/1](http://www.cmaj.ca/cgi/data/171/11/1369/DC1/1) (accessed 2005 May 16).