John P A Ioannidis, Anna-Bettina Haidich, Joseph Lau
Ioannidis J P A, Haidich A, Lau J.
Any casualties in the clash of randomised and observational evidence?
No—recent comparisons have studied selected questions, but we do need more data
BMJ 2001; 322 :879
doi:10.1136/bmj.322.7291.879