There’s an old tale about a Texas “Sharpshooter” that pulls his pistol out of his holster and shoots at the broad side of a barn pretty much at random without aiming. Then he goes up to the barn with a paintbrush and draws a circle around the bullet holes and says: “See, I have perfect aim”. That’s kinda how a lot of cancer clusters are.
People generally get cancer at random (with some exceptions like occupational exposures, gross environmental contamination & genetic risk etc.). But, the laws of statistics state that even when cases of cancer are randomly distributed, there’ll be some groupings that form at random- giving the false appearance that there’s a geographic cluster- when it’s really just random.
Back in the day, our Arizona Cancer Registry calculated cancer rates etc. on a county by county level- but didn’t have any pre-calculated analyses on a smaller scale. That policy led to tons requests for special analyses for smaller areas (with perceived “cancer clusters”)- creating lots of extra work and with little to no public health payoff. So, Dr. Bob England (when he was our State Epi) had an idea to revamp our cancer registry so that we constantly calculated rates in smaller areas of the state. With this uniform approach- we could stop chasing our tail and actually provide some useful public health information. That’s when the (now famous because of medical marijuana) 126 Community Health Analysis Areas (CHAAs) were born. Using CHAAs, we can map cancer rates over time in smaller areas.
Nowadays our Arizona Cancer Registry has a highly interactive website that uses state-of-the-art GIS technology- which lets ordinary folks as well as researchers to access cancer data by CHAA. The website visualizes cancer data with interactive maps, tables and graphs including a rate distribution graph, a time series chart and a rate classification chart. All the elements are linked, so a selected community in one chart or map will be selected in all others. Explore this link to explore the website and its many features- have at it.