In Heike Langenberg's meeting report, “Meteorology: Oscillating opinion” (Nature 408, 924–925; 2000), the “new index” for the North Atlantic Oscillation, attributed to P. Yiou, refers to a poster by V. C. Slonosky and P. Yiou. The index was developed by Victoria Slonosky, Phil Jones and Trevor Davies at the University of East Anglia. Further details can be found in Slonosky, V. C., Jones, P. D. & Davies, T. D. Int. J. Clim. 20, 1874–1897 (2000).