What is known as “point mentality” is a knee-jerk response to what appears to be a problem. We may learn this when we take our child’s temperature and find that it’s high; we are inclined to do something right away—give ibuprofen, orange juice, and bed rest—rather than waiting to see if this is a “trend.”
In fact, sometimes we can’t wait to evaluate patterns in data, but need to respond immediately to a situation. Emergencies require response. But most of the time, we will save time, energy, and other resources by examining data over a period of time and making decisions based on trends or other patterns in the operation of the system itself. The fact that a child fails one third-grade spelling test does not mean that he or she will be a failure in life—or even in spelling.
Every system has variation; some of this is due to the system itself, known as common cause variation; some of it is due to singular incidents or special situations; this is special cause variation. W. Edwards Deming estimated that 94% of problems (or possibilities for improvement) lie with the system as common-cause variation; 6% are special causes. [Out of the Crisis, 315]
Describing variability over a period of time helps one to understand how the system is working, and to predict how it will continue to work in the future. The alternative is a constant tampering with the system, responding to every whim it may have.
