We can’t measure everything, and because we have to limit our measurements, some things invariably fall between the cracks. For example, we tend to measure project performance based on cost, schedule, and scope targets. But these measurements don’t take quality and customer satisfaction into account. If a conflict arises, they lose out. So what should be done? The decomposition approach would add two more measurements, so now we measure cost, schedule, scope, quality and customer satisfaction. Voila! We have turned the iron triangle into an iron pentagon.
When a measurement system has too many measurements the real goal of the effort gets lost among too many surrogates, and there is no guidance for making trade-off among them. The solution is to “Measure UP” that is, raise the measurement one level and decrease the number of measurements. Find a higher-level measurement that will drive the right results for the lower level metrics and establish a basis for making trade-offs. In the example of project metrics above, instead of adding two more measurements we should use a single measurement – the one thing that really matters. Return on investment (ROI) is a possible candidate for projects. Profit and loss models work well for products. If we optimize the one thing that really matters, the other numbers will take care of themselves.
Source: The Seven Principles of Lean Software Development, Mary & Tom Poppendieck, Addison-Wesley