McManus R J, Wilson S, Delaney B C, Fitzmaurice D A, Hyde C J, Tobias R S, Jowett S, Hobbs F D
Department of Primary Care and General Practice, University of Birmingham, Birmingham B15 2TT, UK.
BMJ. 1998 Dec 5;317(7172):1562-3. doi: 10.1136/bmj.317.7172.1562.