What's the problem with poo in the post?

I have finally reached the age where I have sent my poo off in the post to a mysterious lab somewhere in Melbourne.  It got me thinking about the participation rates and the linkages through the "value chain" of the health system.  More screening, leads to more endoscopy, leads to more cancers detected early, leads to improved survival....that is the theory. 

Below is a heat map I have developed based on the national participation rates at SA2 level.  There are some interesting results.

What is going on in the inner south east suburbs of Melbourne? These have lower participation rates than most other areas, yet high socioeconomic status and private health insurance.  My bet is that elective colonoscopy is being used as a screening tool - negating the need for the NBCSP.  This probably explains the high rates reported in the Australian Atlas of Healthcare Variation.