BMJ. 1989 Sep 09;299(6700):669-70. doi: 10.1136/bmj.299.6700.669.
BMJ (Clinical research ed.)
P M Crawford, D I Shepherd
PMID: 2508859 PMCID: PMC1837554 DOI: 10.1136/bmj.299.6700.669 Free PMC Article
[No abstract available.]