TY  - RPRT
TI  - Understanding controlled trials. Crossover trials.
AU  - B Sibbald
AU  - C Roberts
PY  - 1998
DO  - 10.1136/bmj.316.7146.1719
UR  - https://pubmed.ncbi.nlm.nih.gov/9614025/
ID  - 9614025
ER  -