We need to find designs that minimize the error. Our best chances in these cases, if we still believe that it's important to know, they would be randomized trials. Even those may not be able to get us an entirely definitive answer. But at least we know that we're not starting completely off base.
John Ioannidis of Stanford University talks with EconTalk host Russ Roberts about his research on the reliability of published research findings. They discuss Ioannidis's recent study on bias in economics research, meta-analysis, the challenge of small sample analysis, and the reliability of statistical significance as a measure of success in empirical research.