The New Yorker has a very interesting piece about the hazards of publication bias and skewed data in the hard sciences, particularly medicine and biology. Recommended.
Apparently there is a phenomenon in which effect sizes for established causal correlations decrease over time. That is, early studies establishing correlations tend to report much higher effect sizes than later replication studies, and it does not appear this is the result of regression toward the mean. Probably the result of unintentional skewing of data by researchers and of publication bias.