Control Charts and a Visit With My Doctor - Part 1: Monitoring Cholesterol, and Wait Times

Minitab Blog Editor 30 September, 2011

Waiting roomSo I’m in my doctor’s office the other day and he tells me my “LDL” is “out-of-control.”

“What’s an LDL?” I asked.

“I’m glad you asked,” he said. “You see, LDL is the bad cholesterol and you want it to be low.”

“So there’s a good cholesterol?” I asked.

“Yes, it’s called HDL, and yours should be higher.”

“Oh, so the HDL should be higher than the LDL? Kind of like how the UCL is higher than the LCL on a control chart?”

“Not exactly,” he said. “LDL is usually higher than HDL, but your LDL is too high. I’m going to try you on a statin drug.”

“Will that bring my cholesterol under control?” I asked.

“I hope so. We’ll have to monitor it,” he said. “By the way, what’s a control chart?”

“I’m glad you asked,” I said. “A control chart is just a graph that helps you keep tabs on your process and make sure it is not out of control.”

“Out of control, like your cholesterol?” he asked.

“Not exactly,” I said. “A better example might be wait times. I noticed that compared to other doctors’ offices, I didn’t have to wait too long in your lobby. I didn’t even have time to peruse that vintage collection of Sports Illustrated you have out there.”

“Yeah, we actually worked hard on that,” he said. “We had a terrible problem with late arrivals and appointments running over, so we changed our scheduling procedures to reduce the wait times. Seems to have worked pretty well.”

“How do you know?“ I asked.

“You just said so.”

“No, I mean are you monitoring the wait times to make sure they don’t creep up again?”

“Not that I know of.”

“Why not?” I asked. “You’re pretty careful about monitoring the health of your patients. Shouldn’t you monitor the health of your business process? You could use a P chart.”

“Hey, I’m a general practitioner, not a urologist.”


“What’s a P chart?”

“I’m glad you asked,” I said. “A P chart is very simple. You just mark on a chart the proportion of wait times each day that are above the desired maximum.”

“Hmmm. Well, we record the time you check in. And when I sit down with you, that time gets recorded too. So we definitely know how long you were waiting."

“Perfect. If you chart the proportion of wait times that are too long, you can easily see if they start creeping up or go out of control suddenly. That way you’ll know when something is wrong so you can find and fix it.”

“Oh, so ‘P’ is for ‘proportion.’”

“Yeah, what did you think it was for?”

“Nothing,” he said. “So, if I wanted to suggest at the next staff meeting that we try one of these P charts, how would I propose we make it?“

“That’s easy," I said. "I work at Minitab. We make data analysis software that lots of companies use for quality process improvement. In fact, lots of hospitals and other health care companies like yours use Minitab everyday. It has tons of great tools for quality analysis, including the venerable P chart.”

“Well I think that makes a lot of sense. We spent a considerable amount of time and money making the customer experience better. We should definitely try to make sure it stays that way."

He stroked his chin and seemed deep in thought for a moment. Then his eyes brightened and he turned back to me and said, "Let’s see you back here in a couple of months so we can chart your progress.”

He shook my hand and turned to leave with a slightly smug expression on his face that told me:
A) he enjoyed silly puns, and
B) he knew that when he proposed the terrific idea that they use Minitab Statistical Software to monitor their valuable business processes, it would make him the hero of the next staff meeting!

As for me, I left with my a new prescription and high hopes for low cholesterol. But I had a feeling we would speak of this again.

[To be continued …]