Many years ago, my former employer (and precursor to Public Health England or PHE) – the Association of Public Health Observatories, released a series of Excel spreadsheets in which the basic statistical calculations for various funnel plots were described and demonstrated. You can still find these resources online (proportions, rates and DSRs, ISRs and SMRs, counts). If you don’t know what the difference is between a rate, proportion or a count (nor how to identify them), read the accompanying guide here.
Put simply, a funnel plot is a two-axis control chart that takes into account sample size when performing significance testing. It places a measure of variation on the Y-axis and a measure of population (or sample size) on the X-axis. The control limits become tighter as the associated population becomes larger – hence the funnel. This principle can be applied to a variety of measures, albeit with different statistical underpinnings. Read more