These two terms refer to data of known quality that are effective for making the intended decisions because sampling, analytical, and relational uncertainties have been managed to the degree necessary to meet specified goals for decision confidence. Decision quality data can be cost-effectively provided in a number of ways, depending on the decision.

Early in a project, decisions will revolve around developing the conceptual site model (CSM) and testing alternative hypotheses about what contaminants are present, how they got there, and how they are distributed. Broad spectrum fixed laboratory methods may be useful screening tools to evaluate the list of potential contaminants of concern, but data users should realize that the realities of full-suite analysis means that analytical quality will not be the same for each analyte on the list. Further workup is generally required to resolve any analytical inconsistencies and to understand sample representativeness. For example, are the PCBs detected by full-suite SVOC analysis in a couple of samples really a contaminant of concern for the site? Is TCE in the groundwater caused by on-site sources or by migration under the site from off-site sources? The data needed to confidently resolve these types of questions seldom require the lowest possible detection limits or the best analytical precision. Dense sampling (or sampling in the most informative locations) using relatively imprecise field techniques can provide definitive evidence of wide-spread vs. inconsequential contamination or on-site vs. off-site sources. Even if not of "gold-plated" analytical quality, data quality is "acceptable" (i.e., of decision quality) if both sample representativeness and analytical quality are "good enough" to support the decision being made. The field method alone may be able to provide sufficient analytical quality along with sufficient sampling density to produce data effective for making the decision.

On the other hand, most projects hope to eventually achieve clean closure. Regulatory confidence in clean closure decisions and a "no further action" letter requires 1) good delineation of contaminant populations (i.e., a confident CSM) along with 2) rigorous analytical quality that provides the needed quantification limits for specific target analytes. Because of the cost, taking enough samples to get good delineation using fixed laboratory samples is usually cost-prohibitive, so delineation should be accomplished using a less expensive field method. Once the field method confirms a confident CSM, selected samples of known representativeness can be sent for rigorous analysis to demonstrate regulatory compliance. For this kind of decision, decision quality data are only achieved through collaboration between both types of analytical techniques: the field method develops the CSM and manages sampling uncertainties, while the lab method manages remaining analytical and relational uncertainty.