[F]ewer than 2% of all drugs that are investigated by academics in preclinical trials are ultimately approved for sale. A recent study found that just 1 in 5 drugs that were successful after Stage 1 trials made it through the FDA approval process.
Source: Sherry Glied quoted by Timothy Taylor
Also, both authors are very good on why RCTs (randomized controlled trials) rarely produce workable reforms for reducing crime or improving educational results.