Metrics are usually specialized by the subject area, in which case they are valid only within a certain domain and cannot be directly benchmarked or interpreted outside it. This factor severely limits the applicability of metrics, for instance in comparing performance across domains. The prestige attached to them may be said to relate to a 'quantifiability fallacy', the erroneous belief that if a conclusion is reached by quantitative measurement, it must be vindicated, irrespective of what parameters or purpose the investigation is supposed to have.
Examples include academic metrics such as an academic journal's impact factor and bibliometrics; crime statistics; corporate investment metrics, such as earnings per share or Price-to-earnings ratio; economic metrics or economic indicators, such as gross domestic product and the Gini coefficient, which are the subject of econometrics; education metrics, such as grade point average, standardized test scores such as the SAT and College and university rankings; environmental or sustainability metrics and indices; health metrics, such as mortality rate and life expectancy; market metrics such as the Q score; political metrics, such as the United States Presidential approval rating; software metrics; and vehicle metrics such as miles per gallon. In business, they are sometimes referred to as key performance indicators, such as overall equipment effectiveness, or key risk indicators. In the field of Facilities Management, a key metric is the Facility Condition Index, or FCI.