2.2 Cause and Effect Diagram

Let’s talk about another tool. Cause and Effect Diagram. There’s three terms for the same tool. Cause and Effect Diagram or CE Diagram you’ll see it written as sometimes. Fishbone diagram because again, it looks like a fish bone. Or an Ishikawa diagram. Guess what? Ishikawa’s the one who developed it. Cause and effect diagram, it’s a visualization tool for categorizing potential causes of problems, and we’re going to in this tool be looking for root causes. If we look at the cause and effect diagram, it identifies issues that cause our problems versus a Pareto chart, a Pareto chart is going to prioritize those and put those together in a little different visual format. Cause and effect diagram is going to say well, we have something that kinda looks like a fish bone here. The effect is what we have out on the end of this thing, and then we have the various fish bones along the way. A common four category method for this is People, Materials, Machines, and Methods. This is called the four M’s. Materials, Machines, Methods. People, that’s not an M. In a less enlightened time, that was called manpower. Now it’s people. So it’s still referred to mostly as the four M’s. Now we look for causes in here and we go deeper. What’s the cause of something with materials. There’s some material thing that’s causing this problem like we talked about before. Bad car key. Well what about the bad car key? Car key’s fine. It fits into the little slot where you put the key in there. Oh, it’s the chip inside the car key. So we keep asking why, why, why until we finally get to oh, this is the root cause. My brother-in-law couldn’t start the car because there was a bad chip in the key. Fix the chip, everything’s fine. So that’s what we’re looking for. That one little small thing, that’s the cause. The main key root cause of our problem. Here’s a couple of examples of what a fishbone diagram would look like. So we have poor gas mileage. There’s some people issues. People just have some driving problems. I don’t know if you’ve heard about some of the people who drive Priuses and are trying to get the most gas mileage out of it they possibly can. Some of those people are trying to have people drive the cars the best they can. And so they’re saying, drive it barefoot is even better. Do this is even better. Do that is even better, to get one more mile per gallon out of these things. Equipment issues. You may have a car that, when you bought it, got pretty good gas mileage. And now that it’s six years old, it’s not getting such good gas mileage. There’s just some equipment issues with this thing. Measurement. Maybe you just don’t know how to measure mileage very well. You might use the little thing that’s on your odometer that says this is how many miles per gallon you’re getting. Maybe that thing’s kind of worn out. That measurement isn’t good. Instead of doing the old time math way of calculating the miles you’ve driven and then figuring out how much gas you used during those miles. Which means you have to write down mileage every time at the gas pump, as well as how many gallons of gas you’re getting. And then do some math to figure this out. Maybe then we’ll finally get a better look at what our gas mileage actually is. So we’re just looking at, what are the causes of our problem? And then we’ll go back and figure out how to fix those things.