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Volume 14, Issue 8;   February 19, 2014: Scope Creep and the Planning Fallacy

Scope Creep and the Planning Fallacy

by

Last updated: August 8, 2018

Much is known about scope creep, but it nevertheless occurs with such alarming frequency that in some organizations, it's a certainty. Perhaps what keeps us from controlling it better is that its causes can't be addressed with management methodology. Its causes might be, in part, psychological.
A visual illusion

A visual illusion. While staring at the dot in the center of the image, move your head forward and back. You'll see the two rings of quadri­later­als rotate in opposite directions. They don't actually rotate at all, much less in opposite directions, but your visual system tells you that they do. Even after you're aware that this is an illusion, you can't make the illusion "go away." That is also the hallmark of cognitive biases. Even when we're aware of their effects, we can't manage to exercise unbiased judgments. To avoid the effects of a cognitive bias that affects personal judgment in a given situation, we must recruit the assistance of someone (or several someones) who aren't in that situation, and who thus aren't subject to that cognitive bias. Of course, because they could be subject to some other cognitive bias or biases, designing bias-avoidance procedures can be tricky. Image courtesy U.S. National Institute of Environmental Health Sciences.

Google "scope creep" and you get over three million hits. Mission creep gets 700,000. Feature creep also gets over 700,000. That's pretty good for a technical concept, even if it isn't quite "miley" territory (160 million). The concept is known widely enough that anyone with project involvement has probably had first-hand experience with scope creep.

If we know so much about scope creep, why haven't we eliminated it? One simple possible answer: Whatever techniques we're using probably aren't working. Maybe the explanation is that we're psychologically challenged — that is, we, as humans, have a limited ability to detect scope creep, or to acknowledge that it's happening. If that's the case, a reasonable place to search for mechanisms to explain its prevalence is the growing body of knowledge about cognitive biases.

A cognitive bias is the tendency to make systematic errors of judgment based on thought-related factors rather than evidence. For example, a bias known as self-serving bias causes us to tend to attribute our successes to our own capabilities, and our failures to situational disorder.

Cognitive biases offer an enticing possible explanation for the prevalence of scope creep despite our awareness of it, because "erroneous intuitions resemble visual illusions in an important respect: the error remains compelling even when one is fully aware of its nature." [Kahneman 1977] Let's consider one example of how a cognitive bias can make scope creep more likely.

In their 1977 report, Kahneman and Tversky identify one particular cognitive bias, the planning fallacy, which afflicts planners. They The planning fallacy can lead to
scope creep because underestimates
of cost and schedule can lead
decision makers to feel that
they have time and resources
that don't actually exist
discuss two types of information used by planners. Singular information is specific to the case at hand; distributional information is drawn from similar past efforts. The planning fallacy is the tendency of planners to pay too little attention to distributional evidence and too much to singular evidence, even when the singular evidence is scanty or questionable. Failing to harvest lessons from the distributional evidence, which is inherently more diverse than singular evidence, the planners tend to underestimate cost and schedule.

But because the planning fallacy leads to underestimates of cost and schedule, it can also lead to scope creep. Underestimates can lead decision makers to feel that they have time and resources that don't actually exist: "If we can get the job done so easily, it won't hurt to append this piece or that."

Accuracy in cost and schedule estimates thus deters scope creep. We can enhance the accuracy of estimates by basing them not on singular data alone, but instead on historical data regarding organizational performance for efforts of similar kind and scale. And we can require planners who elect not to exploit distributional evidence in developing their estimates to explain why they made that choice.

In coming issues we'll examine other cognitive biases that can contribute to scope creep.  Next in this series Go to top Top  Next issue: Scope Creep, Hot Hands, and the Illusion of Control  Next Issue

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Footnotes

[Kahneman 1977]
Kahneman, D., and A. Tversky. "Intuitive Prediction: Biases and Corrective Procedures," Technical Report PTR-1042-7746, Defense Advanced Research Projects Agency, June, 1977. Also Kahneman, D., and A. Tversky, "Intuitive Prediction: Biases and Corrective Procedures," Management Science, 12, 313-327, (1979). Back

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