Consistent Associations May Be Causal Ones…?

Do you remember the Rain Man movie with Dustin Hoffman and Tom Cruise? Great movie that introduced Savant Syndrome to theater audiences all over the world. The savant syndrome is a rare condition in which persons with autistic disorder or other mental disabilities have extraordinary skills that stand in stark contrast to their overall handicap. There is a very interesting documentary on Kim Peeks who was the inspiration for the movie here. Anyway, last post we talked about strength – one of Bradford Hill’s criteria for causation (see here for a refresher). Today we will talk about consistency, a good qualifier for the often obsessive and ritualistic behaviors of autistic savant persons.




An association between two entities is consistent when results are replicated in multiple studies in different settings using different methods. So if a relationship is causal, we can expect to find it consistently in different studies and among different populations.  This implies that many studies need to be done before meaningful statements can be made about any causal relationship.








A great example of this is the long debated causal relationship between smoking cigarettes and lung cancer. It took hundreds, if not thousands of highly technical studies and many, many publications before a definitive conclusion could be made that cigarette smoking increases the risk of cancer and in a causal manner (see here for a statement from the CDC Surgeon General).  


So be consistent in your smoking cessation and you will consistently avoid the risk of lung cancer…


Next post we will tak about Bradford’s third criterium: specificity.




Relax listening to the very eighties styled theme music to Rain Man and…


… I’ll see you in the blogosphere.




Pascal Tyrrell