1. Evaluating Preference Trials of Oral Phosphodiesterase 5 Inhibitors for Erectile Dysfunction 
John P. Mulhall, Francesco Montorsi 
European Urology 
Volume 49, Issue 1, Pages (January 2006)
DOI: /j.eururo
Copyright © 2005 Elsevier B.V. Terms and Conditions

2. Fig. 1
One-way crossover trials of drugs may introduce several biases, as well as period and carryover effects.
European Urology  , 30-37DOI: ( /j.eururo )
Copyright © 2005 Elsevier B.V. Terms and Conditions

3. Fig. 2
Well designed crossover drug trials can minimize bias and period or carryover effects.
European Urology  , 30-37DOI: ( /j.eururo )
Copyright © 2005 Elsevier B.V. Terms and Conditions