winsorising seems to be incorrect... about funnelplotr

[chrismainey]

Sorry for the delayed reply. I thought I'd be notified of issues posted, but seems I've not got that set up right.

You're describing the winsorisation correctly, but there are two methods of outlier adjustment available in the plot. The 'CQC' method is the one you are describing, which uses a square-root transformation and the winsorisation you describe, that's dealt with a bit earlier in the function:

https://github.com/chrismainey/FunnelPlotR/blob/c9029f5906594f5310ca21f59a29a596e5857369/R/OD_adjust_func.R#L48-L53

The second method uses a natural log-transformation and truncates rather than winsorises (based on the methods in https://digital.nhs.uk/SHMI .

https://github.com/chrismainey/FunnelPlotR/blob/c9029f5906594f5310ca21f59a29a596e5857369/R/OD_adjust_func.R#L123-L128

You can switch between them with the 'method' argument, but the default is 'SHMI'. I've found that, with highly overdispersed data, the winsorization and truncation method can lead to limits that are a bit erratic, so that's why it's not the default.

Let me know if you think it needs more descriptions in the support material though (or alter it yourself and send a pull request if you like). Hope that helps.