Scope Creep and the Planning Fallacy

Google "scope creep" and you get over 10.1 million hits. Mission creep gets 15.6 million. Feature creep also gets over 20.2 million. That's pretty good for a technical concept, even if it isn't quite "miley" territory (222 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 existdiscuss 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  Top    Next Issue

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