The Linear Fallacy

Sep 8th, 2002 by Tony in QSM1

For many years, analysts had seriously overestimated oil recovery from regions, based on early drilling success. They had hypothesized all sorts of explanations for the failure of their modules, but Root and Drew finally demonstrated that the failure of the models could be explained by a selection fallacy: “First, most of the oil and gas discovered in a region is contained in a few large fields; and second, most of the large fields are discovered early in the exploration of the region.”

Obviously, if you drill holes at random, you’re more likely to hit oil somewhere in one of the big fields than in one of the small ones.

The Root-Drew fallacy is committed every day in software development in trying to predict how long testing will take based on early results from testing. The smallest amount of test time is spent on a few easy problems; and second, most of the easy problems are found early in the test cycle. It also explain why so many project as “ninety-nine percent complete” for month after month.

— Jerry Weinberg, Quality

Software Management Vol 1, Chapter 13

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