Improvement Insights Blog
Are Line and Bar Charts Harming Your Customers and Company?
Most people are still using line and bar charts to measure performance. Line and bar charts, especially ones with trendlines harm your customers and your company. They harm patients and hospitals. Here’s why:
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“Hi, I’m Jay Arthur, author of “Lean Six Sigma For Hospitals” and QI Macros [software].
“Are line and bar charts harming your company, your hospital, your whatever (your country, even)? Line charts are really good for tracking overall trends like reduction in infant mortality, increase in world literacy rates, but [they’re] not very good for detecting what’s going on in your company. It’s just {bouncing sound effect} up-y down-y, up-y down-y, but it doesn’t tell you if there’s something special going on; it doesn’t tell you if there’s a signal in all that noise. It just says “Ah, here’s your data.”
“The thing that I found is very difficult is people (often the leadership team) [ask] “Well, why are profits down this month?” “Why is that cost up this month?” Then people go off on wild goose chases to run down things and try and find what’s going wrong. There’s nothing going wrong because it’s just normal variation.
“The thing is, with a control chart… control charts are designed so they can detect signals in the noise, right? Is there something that’s really potentially out of control that you should investigate? Is there a point outside of the control limits? Are there other [points] within there that should only happen three times out of a thousand? If you have 30 data points and it’s happened, maybe we ought to investigate that. This is the great thing about a control chart: it’s smart. It can help you detect signal in the noise of everyday operations. It can tell you to stop wasting time chasing things that aren’t a problem. No more wild goose chases. Let’s go look at things that are statistically unlikely and see if they’re appropriate or not. (Most of the time they’re not, I can tell you.)
“All right… Just because line and bar charts are built into Excel or Google Sheets (or whatever it is), that does not mean that you should use them. They’re the ‘Dumb and Dumber’ of charts, and if you keep using Dumb and Dumber charts, you’re going to make Dumb and Dumber decisions and waste a lot of time doing things that are not necessary.
“I go to all these improvement conferences and I see people look at these charts and say “Oh, that looks like good improvement! Let me take picture of that improvement project, take it back and implement that at my hospital!” No! That stuff’s nonsense… that stuff is nonsense. I’ve looked at enough of it to know it’s questionable.
“The other thing that you see is a lot of line charts, but people put trend lines on them. Excel will fit a trend line to anything; it may not fit very well, but it’ll fit anything. So you see a line, you think “Oh, improvement! Defects down, profit up…” but that’s not it. If you don’t have a goodness of fit metric called ‘R squared’ on there, you have no idea how good that fit is. If it’s not at least 50% or more – 80% is good- 50% or more, it’s nonsense, right?
“Trend lines are such fake news. They can mislead you enormously and make you feel good when it’s not good at all… not good at all. Without R squared you have no idea if that trend line is useful or not, and so anytime you see a trend line on a line chart or a bar chart, guess what? You should [think] “That’s fake news. I don’t believe it.” You need to investigate and make sure that there was actually that level of improvement on that chart. I think Microsoft Excel should not even give you a trend line if it’s below 50% or it should… force it to show the R squared value and say “Hey, not a good fit.” It should tell you something intelligent rather than just fitting it for you.
“So that’s my Improvement Insight: Line and bar charts harm your customers, harm your company, harm your patients, harm your hospital because often they’re just fake news and they don’t help you really detect when there’s a signal in the noise and make some sort of intelligent informed decision.
“Let’s go out and improve something this week… like the use of control charts to monitor your processes so that you can really determine what’s going on in your company.”
