figures of merit
When you compare two cameras, you look at numbers that sum up how good each one is: resolution, zoom range, low-light performance. Analytical methods have their own such scorecard. Figures of merit are the standard, quantitative measures that describe how well a method performs, letting you compare methods on a fair, common footing.
Figures of merit are the set of numerical performance characteristics of an analytical method — including accuracy, precision, sensitivity, selectivity, the limit of detection, the limit of quantitation, and the linear dynamic range. Each captures one facet of quality, and together they paint a full picture of what a method can and cannot do.
They matter because choosing or validating a method comes down to comparing its figures of merit against what the job requires: a method whose detection limit is too high simply cannot do trace work, no matter how precise it is elsewhere. The caveat is that there is no single best method overall — a method strong in one figure (say, sensitivity) may be weak in another (say, speed or cost), so the right choice always depends on the question being asked.
Faced with two methods for measuring mercury, an analyst lays out their figures of merit side by side: method A detects down to 0.1 micrograms per liter but is slow; method B is fast but only down to 5 micrograms per liter. For trace work, A wins.
Figures of merit are a method's scorecard for fair comparison.
No method maxes out every figure of merit at once; they often trade off against each other (and against cost and speed). Picking a method means matching its figures of merit to the demands of the specific problem.