# Not a funnel cake, nor funnel charts, it’s funnel plots!

A funnel cake with powdered sugar, nom nom nom!

Growing up in New England, we had fried dough as the county fair’s mix of white flour, hot oil, and sugar. I wasn’t introduced to its crispier cousin until a trip through Pennsylvania and they became my favorite. But I’m not writing today about funnel cakes – delicious as they are – nor the funnel chart, I’m writing about how to build a funnel plot in Tableau.

What’s a funnel plot? A simple explanation is that a funnel plot is a form of control chart that alters the control limits based on the size of the sample. This is useful when there can be a wide variation in sample sizes between entities, for example when evaluating mortality rates for hospitals where one hospital may have 1,000 cases per year and another 100,000, or performance on a particular physician quality metric such as readmission rates per physician where the panel size may vary from 50 patients to over 1,000.

So far, I haven’t seen anyone else build a funnel plot in Tableau, and hopefully after reading this post you’ll have an understanding of why solving this was as sticky as a funnel cake covered in melted butter & sugar, have a better sense of how Tableau takes in data to draw marks, and be able to build a funnel plot yourself.

# General References

Statistics Done Wrong ebook
Learning Statistics with R psychology text

Basic statistics by Kelly Martin:
http://community.tableausoftware.com/docs/DOC-5269

# Process Control Charts

http://drawingwithnumbers.artisart.org/user-defined-functions-and-process-control-charts/

## Funnel Plots in Tableau

http://drawingwithnumbers.artisart.org/not-a-funnel-cake-nor-funnel-charts-its-funnel-plots/

# R

High-level Tableau Whitepaper http://www.tableausoftware.com/learn/whitepapers/using-r-and-tableau

Tableau’s R KB article
http://kb.tableausoftware.com/articles/knowledgebase/r-implementation-notes

Learning R
http://www.cookbook-r.com

Creating R packages
http://ricardianambivalence.com/2012/07/28/creating-an-r-package-in-10-mins/

SQL Equivalents in R Data Frames
http://vasaptexblog.wordpress.com/2014/01/29/r-simplified-playing-with-dataframes-1/

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