Reliable environmental resource estimates are essential to informed regional scale decisions regarding protection, restoration, and enhancement of natural resources. Reliable estimates depend on objective and representative sampling.Probability-based sampling meets these requirements and provides accuracy estimates (confidence limits). Non-probability-based (judgment or convenience) sampling often is biased, thus less reliable (no accuracy estimates), and potentially misleading. Wecompare results from a probability- and a non-probability-based Secchi transparency sampling of lakes in the northeastern geographic region of the United States and its three primary ecoregions. Results from these samplings are compared on the basis ofsample representativeness relative to the regional lake population and subsequent reliability of lake condition estimates. Statistically derived sampling indicates the northeast lake population median lake size to be about 9.5 (±2.3) ha and the Secchidisk transparency (SDT) to be about 2.4 (±0.4) m. On the basis of judgment sampling estimates, the median SDT for lakes in the same area would be 4.2 m. However, only about 15 of the regional lake population based on statistically designed samplingestimates has a SDT≥4.2 m. Estimate unreliability of this magnitude can have profound effects on lake management decisions. Thus, regional extrapolation of nonprobability-based sampling results should be avoided.
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