A Spoonful of Sugar… Makes the Dose-Response Go Around?

An oldie but a goodie! Haven’t heard of Mary Poppins or her spoonful of sugar? Have a peek here for your dose of the classics. In my most recent set of posts I have been talking about Bradford Hill’s criteria for causality. So far we have covered strength, consistency, specificity, and temporality. Today we are going to talk about biologic gradient or dose-response.

This criterion is pretty easy to understand. An increasing amount of exposure increases a risk in question and with a dose-response relationship present, it is strong evidence for a causal relationship!  

Let’s say you think that being out in the sun in a bathing suit causes your skin to suffer a sunburn. So, the exposure is sunlight and the outcome is sunburn. Based on everyone’s experience, it would certainly appear that the longer you stay out in the sun the greater the risk you will suffer a burn! Your parents have been warning you of this for ever.

However, as with specificity, the absence of a dose-response relationship does not rule out a causal relationship.  A threshold may exist above which a causal relationship is present.  

Next time we will talk about the 6th criterion: plausibility.

Watch one of Simon’s Cat earlier clips Cat-Man-Do and see if you can spot the dose-response…

… and I’ll see you in the blogosphere.

Pascal Tyrrell