Vol. 5, No. 3
from Professor Cleary
Sometimes language can get in the way of real
understanding. The term "out of control" is easily misunderstood as a
pejorative term, suggesting that something is wrong. Other language, such as
"stable" vs. "unstable;" "consistent" vs.
"inconsistent" or "predictable vs. unpredictable" would
convey more clearly the fact that the pattern that Ms. D'Bills sees in her data
is not bad, since a state of being out of control can in fact be a good
Dr. Noah Tahl is correct in asserting that this chart represents an out-of-control situation. On March 2, a run below the mean begins, and continues for 8 consecutive months. In January, there is even a point beyond the lower control limit. But in this case, the value of what is being measured changes the interpretation of the chart. One would want the accounts receivable to go down rather than remain stable, since this trend indicates an expanding (not diminishing) collection rate for the hospital.
So while Dr. Tahl recognizes the textbook pattern here, Ms. D'Bills' intuitive sense that the data represents a positive development is in fact a more accurate interpretation of the pattern.
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