# DATA DREDGING

***Slice your data in enough different ways and you’ll***  
***observe some correlations purely as a result of chance.***  
***Data dredging is the failure to acknowledge that the***  
***correlation was in fact the result of chance.***

Tests for statistical significance only work if you’ve  
defined your hypothesis upfront. Historically, this has been  
a problem with clinical trials where researchers have  
‘data-dredged’ their results and switched what they were  
testing for. It explains why so many results published in  
scientific journals have subsequently been proven to be  
wrong. To avoid this, it’s now becoming standard practice  
to register clinical trials, stating in advance what your  
primary endpoint measure is.