Improvement Insights Blog
An Easy Way to Tell if Data is Variable or Attribute
Six Sigma students are often confused by terminology. Variable and attribute data are often confusing. Calling it measured or counted doesn’t help that much. Here’s a way to explain it that almost everyone can understand quickly.
“Early on when I was teaching Quality Improvement, people kind of struggled with the whole idea of variable and attribute data, and telling them that it was measured and counted didn’t seem to help a lot.
“As a programmer, the way I think about it is: If it has a decimal point, it has to be measured, right? If it’s an integer, it’s most likely counted, right? So it’s most likely counted, but you could have something like length of stay (number of days that a patient stays in a hospital). That could be an integer, right? Or number of days for a payment to be processed or some sort of time measurement but it’s done in integers.
“So when I start to think about that, that’s one of the reasons I created the Control Chart Wizard. If I see a single column of decimals, that’s most likely an XmR chart. If I see multiple columns of decimals, that’s most likely an XbarR or XbarS chart. If I see a column of integers, that could be a c chart or an XmR chart; if the numbers are big it’s probably not a c chart because c charts are supposed to be unlikely, right? So an XmR chart is most likely if there’s bigger numbers and a c chart if they’re smaller numbers. If I have two columns of integers and one’s bigger than the other, that’s probably numerator [and] denominator; that’s a p or a u chart, right?
“So if we start to help people understand that variable is decimals and attribute or counted is integers (and sometimes integers can be variable, but yeah… most of the time they’re not), that I think is a useful separator. Everybody knows what a decimal is and what an integer is. So maybe there’s an easier way to explain these things than the ugly way we’ve been doing it, naming it the official word, right?
“I’m Jay Arthur, author of “Lean Six Sigma for Hospitals” and QI Macros [software]. That’s my Improvement Insight for this week. Let’s make things simpler, all right? Let’s go out and improve something this week.”