| the use of geographic information system (gis) and non-gis methods to assess the external validity of samples postcollection. | external validity is fundamental to veterinary diagnostic investigation, reflecting the accuracy with which sample results can be extrapolated to a broader population of interest. probability sampling methods are routinely used during the collection of samples from populations, specifically to maximize external validity. nonprobability sampling (e.g., of blood samples collected as part of routine surveillance programs or laboratory submissions) may provide useful data for further posthoc epidemi ... | 2009 | 19737758 |