Bye, Bye American Pie (Charts)

I admit it – I didn’t embrace the Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS-pronounced “H-Caps”) survey when it was first introduced. I thought it was too simplistic to address the extraordinarily complex issues in our healthcare system. Okay, truth be told — I was a “complexity snob” and (hold the phone and mark the calendar) I was dead wrong.

As the first national, standardized, publicly reported survey of patients’ perspectives of hospital care, HCAHPS data is an important and valuable tool in institution’s efforts to improve the delivery of care. It is also an important resource for patients who wish to understand how well an institution is performing on important measures such as communicating with patients – – which scientific studies and Dr. Phil remind us time and again are essential to improving everything in life.

But here is the problem — even institutions with outstanding scores on physician and nurse communication don’t communicate these survey results very well to the public i.e., the patients and families they serve. Rather, all too frequently I find that institutions show this data on their public facing websites using pie charts. And although it would be a bit over the top to say that pie charts are evil, it would be true to say that they are a bad choice for displaying data.

The standard argument in favor of pie charts is that they show “part-to-whole” relationships optimally, but in fact a bar chart can do the job a whole lot better.

Take a look at the following pie charts of patient satisfaction scores — notice how you have to orient yourself to the colors and the labels and you have to look back and forth to make any sort of comparisons between the measures. It is not easy to see at a glance where the institution is doing a good job and where they could improve.

Additionally, the differences in the size of the parts of the pie charts are hard to compare — you have to hold information in your mind and then do a bit of mental and visual gymnastics to try and discern variances and patterns.

Pie Charts of Patient Satisfaction

And, did you notice another problem with the pie charts? Look closely. The labels got switched somewhere in the reporting of the information — red, blue and green mean something different on each of the measures. And because of the way the labels are formatted the pie chart for the measure “Communication with Physicians” is smaller than all of the other charts.

As Edward Tufte wrote in his classic book The Visual Display of Quantitative Information, “the only worse design than a pie chart is several of them.”

Now consider the following display of the information in a horizontal bar graph.

Pie Chart Redesigned to Bar Graph

By listing the categories of responses on the Y axis just once the graph becomes less cluttered and by repeating the same scale on the X axis for each measure the viewer is easily oriented to the information – it is clear and consistent across all of the measures.

And now, at a glance, the viewer can see the ratio of responses for each measure and they can also see how in the overarching category of communication the institution is performing. It is clear, simple and effortless.

So remember the sage words of my friend, colleague and data visualization expert Stephen Few to “Save the Pies for Desert.”

Oh yeah, there is a visual for that.

Picture of Pie Eaten and Yet to be Eaten
Source: Edward Tufte August 9, 2009

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