Gilb's Law

Gilb’s Law responds to the paralysis that Goodhart’s Law can cause. This law asserts that even an approximate or indirect measurement is better than none. When something is essential (performance, customer satisfaction, code maintainability), you should attempt to measure it, because otherwise you have no objective feedback.

Gilb’s Law is a good reply to the statement “this aspect is unmeasurable so we won’t try.” For example, measuring “code quality” is difficult, but you can measure indicators such as cyclomatic complexity, lint warnings, or defect rates as partial indicators. More such indicators can paint the bigger picture.

Those metrics won’t be perfect, but Gilb’s Law suggests that having them gives you some insight and a starting point for improvement, which is better than having no clue at all.

• It is better to have some data or metric on a phenomenon than to be completely blind, as long as you understand the metric's limitations.
• In contrast to Goodhart's Law, which warns about misuse of metrics, Gilb's Law reminds us not to throw out metrics entirely.
• Start with a basic measure and refine it over time. The act of measuring helps teams focus and identify trends.
• Even an approximate or indirect measurement is better than none.