As a customer, the worst experience I can imagine is being a casualty of process variation. 'It doesn't seem that bad,' you may be thinking to yourself. Just remember back to the last time you:
- went grocery shopping only to select the slowest teller in the store
- received a haircut that was shorter or longer than usual, and definitely not what you asked for
- decided to go shoe shopping, but got stuck with the most ignorant salesperson available
You can probably come up with a short list of your own experiences without thinking too hard, but you can also probably remember picking the fastest line in the grocery store, receiving a perfect haircut and being ecstatic with your salesperson's knowledge. That was a great feeling, wasn't it?
Let's examine a few ways to help us evaluate variation in processes. First, it's important to put yourself in the right frame of mind - imagine that your children have been whining for pizza all day, and on your way home you stop by your local pizza parlor to order a pizza that you (and your kids) are waiting for. Consider the general concept of variation by examining the preparation time (in minutes) of 10 pizzas being prepared by your two local pie shops. The times are listed below.
| ABC Pizzeria | 6.5 | 6.6 | 6.7 | 6.8 | 7.1 | 7.3 | 7.4 | 7.7 | 7.7 | 7.7 |
| XYZ Pizza To Go | 4.2 | 5.4 | 5.8 | 6.2 | 6.7 | 7.7 | 7.7 | 8.5 | 9.3 | 10.0 |
If we use common statistical tools, such as mean, median, mode and midrange, we get the following results:
| | ABCPizzeria | XYZ Pizza To Go |
| Mean | 7.15 | 7.15 |
| Median | 7.20 | 7.20 |
| Mode | 7.7 | 7.7 |
| Midrange | 7.10 | 7.10 |
You can see from these results that the two pizza parlors have the same measures of central tendency, so, on average, customers wait the same amount of time for pizzas at the two restaurants. Based on these measurements alone, we cannot see any distinguishable difference between the two processes.
If we return to the original data points, however, we can see a very distinguishable difference: ABC Pizza has preparation times with much less variation than the times for XYZ Pizza. If all other characteristics of the pizza (taste, temperature, size, topping quality, service friendliness, etc.) are equal, customers are likely to prefer the ABC Pizza where they will not become annoyed by being the one person whose pizza preparation time is much slower than the others.
By inspecting and comparing the differences in variation between the preparation times of the two pizza companies, we can get a sense for the variation. But in business, we need more than a sense - we need to measure and quantify the process variation. For this reason, we are going to display the use of two tools: range and standard deviation.
Next Page > Range: The Easiest Measure of Variation
Page 3 > Standard Deviation: Arguably The Most Important Variation Measure
