Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
An editorial error occurred in this letter (28 March, pp 1021-2). The letter was attributed to P McCormack et al, but in fact the first author was James P McCormack.
