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W. Scott Overton

Bio: W. Scott Overton is an academic researcher from Oregon State University. The author has contributed to research in topics: Sampling (statistics) & Systematic sampling. The author has an hindex of 10, co-authored 25 publications receiving 406 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, spring base flow chemistry was surveyed in a probability sample of 500 stream reaches representing a population of 64,300 reaches (224,000 km) and approximately half of the streams had acid neutralizing capacity (ANC) ≤ 200 μeq L−1.
Abstract: To assess the regional acid-base status of streams in the mid-Atlantic and southeastern United States, spring base flow chemistry was surveyed in a probability sample of 500 stream reaches representing a population of 64,300 reaches (224,000 km). Approximately half of the streams had acid-neutralizing capacity (ANC) ≤ 200 μeq L−1. Acidic (ANC ≤ 0) streams were located in the highlands of the Mid-Atlantic region (southern New York to southern Virginia, 2330 km), in coastal lowlands of the Mid-Atlantic (2600 km), and in Florida (462 km). Acidic streams were rare (less than 1%) in the highlands of the Southeast. Inorganic monomeric aluminum (Alim) concentrations were highest in acidic streams of the Mid-Atlantic Highlands where over 70% of the acidic streams had Alim greater than 100 μg L−l, a concentration above which deleterious biological effects have frequently been reported. Dissolved organic carbon concentrations were much higher in lowland coastal streams, compared with inland streams. Our data support a hypothesis that atmospheric sources and watershed retention control regional patterns in streamwater sulfate concentrations. Most stream watersheds retain the vast majority of the total nitrogen loading from wet deposition. The data suggest, however, that some deposition nitrogen may be reaching streams in the Northern Appalachians. These results show that acidic surface waters are found outside the glaciated northeastern portions of the United States and that watershed sulfate retention is not sufficient to prevent acidic conditions in some Mid-Atlantic Highlands streams.

68 citations

Journal ArticleDOI
TL;DR: The Horvitz-Thompson theorem as mentioned in this paper offers a needed integrating perspective for teaching the methods and fundamental concepts of probability sampling, and helps to avoid some common stumbling blocks of beginning students.
Abstract: Courses in sampling often lack a coherent structure because many related sampling designs, estimators, variances, and variance estimators are presented as separate cases. The Horvitz-Thompson theorem offers a needed integrating perspective for teaching the methods and fundamental concepts of probability sampling. Development of basic concepts in sampling via this approach provides the student with tools to solve more complicated problems, and helps to avoid some common stumbling blocks of beginning students. Examples from natural resource sampling are provided to illustrate applications and insight gained from this approach.

57 citations

Journal ArticleDOI
TL;DR: Long-term environmental monitoring places a set of demands on a sampling strategy not present in a survey designed for a single time period, and the sampling strategy must be capable of adapting to changes while maintaining its identification as a probability sample and its capacity to detect trends that span the update occasions.
Abstract: Long-term environmental monitoring places a set of demands on a sampling strategy not present in a survey designed for a single time period. The inevitability that a sample will become out of date must be a dominant consideration in planning a long-term monitoring programme. The sampling strategy must be able to accommodate periodic frame update and sample restructuring in order to address changes in the composition of the universe and changes in the perception of issues leading to new questions and concerns. The sampling strategy must be capable of adapting to such changes while maintaining its identification as a probability sample and its capacity to detect trends that span the update occasions. These issues are examined with respect to sub-population estimation, post-stratification via conditioning, and sample enlargement and reduction. Design features that involve complex sample structure create potentially serious difficulties, whereas an equal probability design permits greater adaptability and flexibility. Structure should be employed sparingly and in awareness of its undesirable effects.

50 citations

Book ChapterDOI
TL;DR: Methods of probability sampling provide a rigorous protocol by which scientifically reliable information on environmental issues may be obtained, and practical implications of a few standard designs useful in environmental sampling are discussed.
Abstract: Methods of probability sampling provide a rigorous protocol by which scientifically reliable information on environmental issues may be obtained. We review fundamentals of probability sampling from the perspective of monitoring environmental resources. We first describe basic concepts and definitions of sampling, such as the sampling universe, population, and design-based inference. As the natural, general estimator for probability sampling designs, the Horvitz-Thompson estimator provides the basis of a coherent strategy of consistent estimation. When auxiliary information is available, difference, ratio, and regression estimators are viable alternatives to the Horvitz-Thompson estimator, providing enhanced precision in many circumstances. Rather than repeat descriptions of basic sampling designs available in many texts, we discuss practical implications of a few standard designs useful in environmental sampling. Topics in spatial sampling and monitoring over time are discussed, as are the role and implications of analytic uses of surveys.

44 citations

Journal ArticleDOI
TL;DR: In this paper, a tessellation-stratified design was proposed for sampling environmental resources in the Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) and evaluated under various surface model representations of the continuous response variable.
Abstract: Precision of systematic designs for sampling continuous response variables defined over a continuous spatial region have been extensively investigated. Estimation of variance, particularly for triangular grids, has been given less attention. Two of the designs proposed for sampling environmental resources in the Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) are based on a triangular grid. Implementation of either design requires derivation and evaluation of a variance estimator adequate for the purposes of EMAP. The performance of the proposed variance estimator was assessed under various surface model representations of the continuous response variable. Of the designs examined, a tessellation-stratified design permitted better estimation of variance, and was generally more precise, than a strict systematic design.

41 citations


Cited by
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6,278 citations

Journal ArticleDOI
TL;DR: The more recent concepts of point equilibrium and static stability, which characterize the classical equilibrium paradigm in ecology, are traceable to the assumptions implicit in "balance of nature" as mentioned in this paper, which has failed not only because equilibrium conditions are rare in nature, but also because of our past inability to incorporate heterogeneity and scale multiplicity into our quantitative expressions for stability.
Abstract: A common assumption historically in ecology is evident in the term "balance of nature." The phrase usually implies that undisturbed nature is ordered and harmonius, and that ecological systems return to a previous equilibrium after disturbances. The more recent concepts of point equilibrium and static stability, which characterize the classical equilibrium paradigm in ecology, are traceable to the assumptions implicit in "balance of nature." The classical equilibrium view, however, has failed not only because equilibrium conditions are rare in nature, but also because of our past inability to incorporate heterogeneity and scale multiplicity into our quantitative expresssions for stability. The theories and models built around these equlibrium and stability principles have misrepresented the foundations of resource management, nature conservation, and environemtnal protection. In this paper, we sysntesize recent developments that advance our understandings of equilibrium vs. nonequilibrium, homogeneity vs....

1,179 citations

Journal ArticleDOI
TL;DR: In this paper, a unified strategy for selecting spatially balanced probability samples of natural resources is presented, which is based on creating a function that maps two-dimensional space into onedimensional space, thereby defining an ordered spatial address.
Abstract: The spatial distribution of a natural resource is an important consideration in designing an efficient survey or monitoring program for the resource. Generally, sample sites that are spatially balanced, that is, more or less evenly dispersed over the extent of the resource, are more efficient than simple random sampling. We review a unified strategy for selecting spatially balanced probability samples of natural resources. The technique is based on creating a function that maps two-dimensional space into one-dimensional space, thereby defining an ordered spatial address. We use a restricted randomization to randomly order the addresses, so that systematic sampling along the randomly ordered linear structure results in a spatially well-balanced random sample. Variable inclusion probability, proportional to an arbitrary positive ancillary variable, is easily accommodated. The basic technique selects points in a two-dimensional continuum, but is also applicable to sampling finite populations or one-dimension...

1,082 citations

Journal ArticleDOI
TL;DR: In this paper, the authors use point processes or marked point processes (PPP) to model the characteristics of a single-tree forest, where the points are tree locations and the marks are tree characteristics such as diameter at breast height or degree of damage by environmental factors.
Abstract: Forestry statistics is an important field of applied statistics with a long tradition. Many forestry problems can be solved by means of point processes or marked point processes. There, the "points" are tree locations and the "marks" are tree characteristics such as diameter at breast height or degree of damage by environmental factors. Point pro- cess characteristics are valuable tools for exploratory data analysis in forestry, for describing the variability of forest stands and for under- standing and quantifying ecological relationships. Models of point pro- cesses are also an important basis of modern single-tree modeling, that gives simulation tools for the investigation of forest structures and for the prediction of results of forestry operations such as plantation and thinning.

498 citations

Journal ArticleDOI
TL;DR: This paper presents a spatially explicit hierarchical modeling approach to studying the patterns and processes of heterogeneous landscapes, and describes the general structure of a hierarchical urban landscape model (HPDM-PHX) which is developed using this modeling approach.

490 citations