Improvement Insights Blog
Line Charts with Trend Lines are often Fake News
Ever seen a line chart with a trend line that implies there was great improvement? Probably not. Here’s why:
“Hi, I’m Jay Arthur, author of “Lean Six Sigma For Hospitals” and QI Macros [software].
“If you’re listening to anything in the news, they always talk about “fake news,” right? Fake news: somebody made stuff up. But in my experience, when I’m wandering around [seeing] all of these presentations and poster presentations at trade shows and stuff, I keep seeing all these line charts with trend lines in them. “Oh look! We have a trend line! It’s reducing whatever it is,” right? Or “It’s increasing whatever it is.” But it doesn’t have a “goodness of fit” metric on it.
“I want you to consider that any time you see a line chart with a trend line on it that does not have the “r squared goodness of fit” metric on it (so you can tell if it actually is a good fit or not), you should consider that to be “fake news.” They’re pretending they made an improvement! Until such time as you put that into a control chart and you can see where it actually stepped down, I think you should consider that to be fake news. Don’t trust it.
“Now, the reason I know this is because I’ve taken a number of things that I have seen at these trade shows where they left me the numbers so I know what the numbers are, and then I actually [recreated the chart] and found out that the… goodness of fit metric was less than fifty percent… sometimes thirty percent. Not very good at all. So I wouldn’t want to stake my reputation on that because that would be silly, all right?
“So that’s my Improvement Insight for this week: Stop using line charts with trend lines, they are dumb and they are misleading; they are often fake news. Start using control charts, and there’s plenty of software like QI Macros out there to draw it. If you’re not using mine, use somebody else’s, but start using control charts! It’ll change your life and how you run your business, and it’ll simplify all the noise that is out there in your organization… and you will not be misleading people.
“Let’s create a hassle-free America; hassle-free healthcare. Let’s go out and improve something this week.”
