Some recent studies have analyzed the percentage of research that is reproducible. E.g. Prinz, F.; Schlange, T.; Asadullah, K. (2011). "Believe it or not: How much can we rely on published data on potential drug targets?". Nature Reviews Drug Discovery 10 (9): 712. doi:10.1038/nrd3439-c1. PMID 21892149. found that found that 65% of medical studies were inconsistent when re-tested, and only 6% were completely reproducible.
I wonder how research reproducibility in medicine has evolved over time.