1. Google. http://www.google.com [accessed 17.01.2013].
2. PubMed. http://www.ncbi.nlm.nih.gov/pubmed [accessed 17.01.2013].
3. How does your searching grow? A survey of search preferences and the use of optimal search strategies in the identification of qualitative research;Grant;Health Information & Libraries Journal,2004
4. Assessing the quality of research;Glasziou;British Medical Journal,2004
5. A concise guide to clinical trials;Hacksaw,2009