Showing papers on "Sampling (statistics) published in 1991"

Practical Statistics for Field Biology

Abstract: Measurement and Sampling Concepts. Processing Data. Presenting Data. Measuring the Average. Measuring Variability. Probability. Probability Distributions as Models of Dispersion. The Normal Distribution. Data Transformation. How Good are Our Estimates? The Basis of Statistical Testing. Analysing Frequencies. Measuring Correlations. Regression Analysis. Comparing Averages. Analysis of Variance - ANOVA. Multivariate Analysis. Appendices. Bibliography and Further Reading. Index.

The Design and Administration of Mail Surveys

Abstract: For reasons of cost and ease of implementation, mail surveys are more frequently used for social research than are either telephone or face-to-face interviews. In this chapter, the last two decades of research aimed at improving mail survey methods are examined. Discussion of this research is organized around progress made in overcoming four important sources of error: sampling , noncoverage, measurement, and nonresponse. Progress has been especially great in improving response rates as a means of reducing nonresponse error. Significant progress has also been made in finding means of overcoming measurement error. Because mail surveys generally present few, if any, special sampling error problems, little research in this area has been conducted. The lack of research on noncoverage issues is a major deficiency in research to date , and noncoverage error presents the most significant impediment to the increased use of mail surveys. The 1990s are likely to see increased research on mail surveys, as efforts ar...

A simplified general method for cluster-sample surveys of health in developing countries.

Abstract: General guidelines are presented for the use of cluster-sample surveys for health surveys in developing countries. The emphasis is on methods which can be used by practitioners with little statistical expertise and no background in sampling. A simple self-weighting design is used, based on that used by the World Health Organization's Expanded Programme on Immunization (EPI). Topics covered include sample design, methods of random selection of areas and households, sample-size calculation and the estimation of proportions, ratios and means with standard errors appropriate to the design. Extensions are discussed, including stratification and multiple stages of selection. Particular attention is paid to allowing for the structure of the survey in estimating sample size, using the design effect and the rate of homogeneity. Guidance is given on possible values for these parameters. A spreadsheet is included for the calculation of standard errors.

The theory of bandpass sampling

Abstract: The sampling of bandpass signals is discussed with respect to band position, noise considerations, and parameter sensitivity. For first-order sampling, the acceptable and unacceptable sample rates are presented, with specific discussion of the practical rates which are nonminimum. It is shown that the minimum sampling rate is pathological in that any imperfection in the implementation will cause aliasing. In applying bandpass sampling to relocate signals to a base-band position, the signal-to-noise ratio is not preserved owing to the out-of-band noise being aliased. The degradation in signal-to-noise ratio is quantified in terms of the position of the bandpass signal. For the construction of a bandpass signal from second-order samples, the cost of implementing the interpolant (dynamic range and length) depends on Kohlenberg's sampling factor (1953) k, the relative delay between the uniform sampling streams. An elaboration on the disallowed discrete values of k shows that some allowed values are better than others for implementation. >

Evaluating the accuracy of sampling-based approaches to the calculation of posterior moments

Abstract: Data augmentation and Gibbs sampling are two closely related, sampling-based approaches to the calculation of posterior moments. The fact that each produces a sample whose constituents are neither independent nor identically distributed complicates the assessment of convergence and numerical accuracy of the approximations to the expected value of functions of interest under the posterior. In this paper methods for spectral analysis are used to evaluate numerical accuracy formally and construct diagnostics for convergence. These methods are illustrated in the normal linear model with informative priors, and in the Tobit-censored regression model.

SYN-TAX IV. Computer Programs for Data Analysis in Ecology and Systematics

Abstract: This new release of the package contains 27 FORTRAN and 4 BASIC programs written for IBM-PC and compatible machines and Apple Macintosh II, Plus and SE personal computers. Widely used standard multivariate methods and specific data analytical techniques, some of them suggested by the author, are represented in the package. The procedures programmed include hierarchical and non-hierarchical clustering, fuzzy classifications, block clustering, ordination, character ranking, comparison of classifications and ordinations, consensus methods, Monte Carlo simulation of distributions of partition agreement, simulated sampling based on digitized point patterns, and information theory functions for evaluating species assemblages. This paper gives general information on the programs; technical details are presented in the user’s manual.

Epidemiologic studies utilizing surveys: accounting for the sampling design.

Abstract: BACKGROUND. Since large-scale health surveys usually have complicated sampling schemes, there is often a question as to whether the sampling design must be considered in the analysis of the data. A recent disagreement concerning the analysis of a body iron stores-cancer association found in the first National Health and Nutrition Examination Survey and its follow-up is used to highlight the issues. METHODS. We explain and illustrate the importance of two aspects of the sampling design: clustering and weighting of observations. The body iron stores-cancer data are reanalyzed by utilizing or ignoring various aspects of the sampling design. Simple formulas are given to describe how using the sampling design of a survey in the analysis will affect the conclusions of that analysis. RESULTS. The different analyses of the body iron stores-cancer data lead to very different conclusions. Application of the simple formulas suggests that utilization of the sample clustering in the analysis is appropriate, but that a...

Models for truncated counts

Abstract: SUMMARY This paper examines a class of maximum-likelihood regression estimators for count data from truncated samples. Estimators for the truncated Poisson and negative binomial distributions are illustrated. Simulation results are given to illustrate the magnitude of the bias that may result from the failure to account for overdispersion in truncated samples. An empirical application based upon the number of recreational fishing trips taken by a sample of Alaskan fishermen is provided. the number of bus trips taken per week and other variables which might be related to that behaviour, such as attitudinal and demographic variables. Given these data we seek to construct a model of the number of weekly bus trips taken as a function of various exogenous variables, some of which are under the control of the public transit authority. Due to the choice-based sampling scheme employed, no observations are made of individuals making zero bus trips, since a criterion for sample inclusion is that at least one bus trip be made. The dependent variable in our model, the number of bus trips taken that week, is truncated at zero, taking on only positive values. More generally, two common types of sampling schemes are likely to give rise to samples of truncated counts: surveys which ask 'participants' about the number of 'participation occasions' and samples drawn from administrative records where inclusion in such a database is predicated on having engaged in the activity of interest. Examples of the first type include on-site sampling plans, surveys of owners of a particular home appliance (e.g. from warranty

Spectrally optimal sampling for distribution ray tracing

Abstract: Nonuniform sampling of images is a useful technique in computer graphics, because a properly designed pattern of samples can make aliasing take the form of high-frequency random noise. In this paper, the technique of nonuniform sampling is extended from two dimensions to include the extra parameter dimensions of distribution ray tracing. A condition for optimality is suggested, and algorithms for approximating optimal sampling are developed. The technique is demonstrated at low sampling densities, so the characteristics of aliasing noise are clearly visible. At supersampling rates, this technique should move noise into frequencies above the passband of the pixel-reconstruction filter.

Sampling and reconstruction with adaptive meshes

Abstract: An approach to visual sampling and reconstruction motivated by concepts from numerical grid generation is presented. Adaptive meshes that can nonuniformly sample and reconstruct intensity and range data are presented. These meshes are dynamic models which are assembled by interconnecting nodal masses with adjustable springs. Acting as mobile sampling sites, the nodes observe properties of the input data, such as intensities, depths, gradients, and curvatures. Based on these nodal observations, the springs automatically adjust their stiffnesses so as to distribute the available degrees of freedom of the reconstructed model in accordance with the local complexity of the input data. The adaptive mesh algorithm runs at interactive rates with continuous 3-D display on a graphics workstation It is applied to the adaptive sampling and reconstruction of images and surfaces. >

Designing and Testing Sampling Protocols to Estimate Biodiversity in Tropical Ecosystems

Abstract: Sampling methods to estimate total species richness of a defined area (conservation unit, national park, field station, "community") will play an important role in research on the global loss of biodiversity. Such methods should be fast, because time is of the essence. They should be reliable because diverse workers will need to apply them in diverse areas to generate comparable data. They should also be simple and cheap, because the problem of extinction is most severe in developing tropical countries where the scientific and museum infrastructure is often still rudimentary. In the past, two scientific fields have been mainly responsible for providing such data: systematics and community ecology. Simplistically summarized, samples collected by systematists better represent the species richness in an area but are intractable statistically, whereas the analysis of samples collected to answer ecological questions is usually straightforward but often poorly represents the total fauna. The two approaches are complementary and we propose a set of methods that seeks the optimal compromise. We applied these methods to sample and estimate species richness of Araneae in Bolivia, but we present criteria so that the methods can be modified for other broadly similar groups. We describe the methods used, present preliminary analyses of the effect of four variables (site, collecting method, collector, and time of day) on total number of adult individuals taken, and discuss analytical approaches that employ such data to estimate total species richness. We also present data from Peruvian canopy fogging samples to show that estimates of species richness of diverse tropical arthropod taxocenes are obtainable in principle.

A Monte Carlo Study of rainfall sampling effect on a distributed catchment model

Abstract: A Monte Carlo study of a physically based distributed-parameter hydrologic model is described. The catchment model simulates overland flow and streamflow, and it is based on the kinematic wave concept. Soil Conservation Service curves are used to model rainfall excess within the basin. The model was applied to the Ralston Creek watershed, a small (7.5 km2) rural catchment in eastern Iowa. Sensitivity of the model response with respect to rainfall-input spatial and temporal sampling density was investigated. The input data were generated by a space-time stochastic model of rainfall. The generated rainfall fields were sampled by the varied-density synthetic rain gauge networks. The basin response, based on 5-min increment input data from a network of high density with about 1 gauge per 0.1 km2, was assumed to be the “ground truth,” and other results were compared against it. Included in the study was also a simple lumped parameter model based on the unit hydrograph concept. Results were interpreted in terms of hydrograph characteristics such as peak magnitude, time-to-peak, and total runoff volume. The results indicate higher sensitivity of basin response with respect to the temporal resolution than to the spatial resolution of the rainfall data. Also, the frequency analysis of the flood peaks shows severe underestimation by the lumped model. This may have implications for the design of hydraulic structures.

Sampling and Analysis of Insect Populations

Abstract: Presentation des methodes d'etude des populations d'insectes basees sur l'analyse des modeles de distribution spatiale, sur des procedures d'echantillonnage et sur l'analyse des facteurs clefs

Environmental Sampling and Analysis: A Practical Guide

Abstract: ENVIRONMENTAL SAMPLING. Introduction to Environmental Sampling. PLANNING AND SAMPLING PROTOCOLS. Data Quality Objectives Affect All Aspects of Planning. Basic Considerations of Planning. Good Sampling Protocols Document Planning. Basic Sampling Approaches. Planning Includes Assessing Migration of Pollutants. Planning Includes Selecting Appropriate Sampling Devices. Composite Sampling Must Be Planned Carefully. Safety Plans Reduce Chemical Exposure and Liability. QUALITY ASSURANCE AND QUALITY CONTROL. Sampling Considerations. Defining Blank Sample Requirements. Using Blanks. Background (Control) Sample Selection. SAMPLING WATER MATRICES. Obtaining Representative Samples. Selecting Sampling Devices. Common Sampling Problems. Sample Preservation. SAMPLING AIR MATRICES. Obtaining Representative Samples. Selecting Sampling Devices. Common Sampling Problems. Influence of Meteorology and Topography on Sampling Air. Topography Effects. SAMPLING BIOLOGICAL MATRICES. Obtaining Representative Samples. Common Sampling Problems. Sample Preservation. SAMPLING SOLIDS, LIQUIDS, AND SLUDGES. Obtaining Representative Samples. Selecting Sampling Devices. Common Sampling Problems. Sample Preservation. ENVIRONMENTAL ANALYSIS. Introduction to Environmental Analysis. PLANNING ANALYTICAL PROTOCOLS. QUALITY ASSURANCE AND QUALITY CONTROL. Quality Assurance. Quality Control. Quality Assessment. Measurement Variability. Verification and Validation. Precision and Accuracy. ANALYTICAL MEASUREMENTS. Definition of the Data Set. Calibration and Standardization. Preparation of Samples. Recovery. Interferences. DOCUMENTATION AND REPORTING. Documentation. Data Generation Versus Data Use. Reporting by Laboratories. Relative Bias at Low Concentration Levels. Reporting by Users. Limit of Quantitation (LOQ). Guidelines for Reporting and Presenting Data. Guidelines for Handling Data. Final Comments. ACKNOWLEDGEMENTS. REFERENCES. OTHER USEFUL SOURCES OF INFORMATION.

Sampling and integration of near log-concave functions

Abstract: Sampling and Integration of Near Log-Concave Functions David Applegate* Ravi Kannan* An important class of functions that arise in statistics and other areas are the log-concave functions. Here we provide the first polynomial time algorithm to generate samples from a given log-concave distribution. The algorithm is fairly simple and natural; it is the proof of its fast convergence that is new. To this end, we prove a general isoperimetric inequality for convex sets and use this together with recent developments in the theory of rapidly mixing Markov chains. We use our sampling algorithm to develop an algorithm for integrating log-concave functions. As one application, we are able to develop an algorithm for approximating the volume of convex bodies given by an oracle; we do so by enclosing the given body in a cube, defining a log-concave function that is 1 on the body and exponentially falls off outside, and integrating this function. This a.llo ws us to avoid one of the complications in prior algorithms for computing volumes – dealing with sharp corners – and results in an algorithm which is faster than previous algorithms.

Solid sampling in electrothermal atomic absorption spectrometry using commercial atomizers. A review

Abstract: 3 Slurry Sample Introduction 3.1 Preparation and Mixing of Slurries 3.1.1 Use of stabilizing agents 3.1.2 Magnetic stirring and vortex mixing 3.1.3 Ultrasonic agitation 3.1.4 Gas mixing of slurry 3.1.5 Pre-digestion of slurry 3.1.6 Electric dispersion in a condensed medium 3.2 Influence of Particle Size 3.3 Influence of Slurry Concentration 3.4 Chemical Modification 3.5 Calibration 3.6 Applications of Slurry Sample Introduction

Handbook of Techniques for Aquatic Sediments Sampling

Abstract: Introduction, A. Mudroch and S.D. MacKnight Project and Data Review, A. Mudroch and S.D. MacKnight Selection of Bottom Sediment Sampling Stations, S.D. MacKnight Bottom Sediment Sampling, A. Mudroch and S.D. MacKnight Sampling the Settling and Suspended Particulate Matter, F. Rosa, J. Bloesch, and D.E. Rathke Sediment Preservation, Processing, and Storage, A. Mudroch and R.A. Bourbonniere Sediment Pore Water Sampling, D.D. Adams Case Studies, J.M. Azcue, J.R.D. Guimaraes, A. Mudroch, P. Mudroch, and O. Malm

Tissue sampling device

Abstract: A device for tissue sampling by thick needle punctuation including a needle assembly including a hollow first needle and second needle extending through the hollow first needle. The needle assembly is contained in a housing having an opening through which the needles extend. Compressed springs in the housing are caused to expand to urge the needles away from the housing during the sampling of tissue. A rod is provided extending from the housing to simultaneously place the springs in a compressed condition.

General sampling theorems for functions in reproducing kernel Hilbert spaces

Abstract: In this paper we prove general sampling theorems for functions belonging to a reproducing kernel Hilbert space (RKHS) which is also a closed subspace of a particular Sobolev space. We present details of this approach as applied to the standard sampling theory and its extension to nonuniform sampling. The general theory for orthogonal sampling sequences and nonorthogonal sampling sequences is developed. Our approach includes as concrete cases many recent extensions, for example, those based on the Sturm-Liouville transforms, Jacobi transforms, Laguerre transforms, Hankel transforms, prolate spherical transforms, etc., finite-order sampling theorems, as well as new sampling theorems obtained by specific choices of the RKHS. In particular, our setting includes nonorthogonal sampling sequences based on the theory of frames. The setting and approach enable us to consider various types of errors (truncation, aliasing, jitter, and amplitude error) in the same general context.

Design and inference in finite population sampling

Abstract: A Unified Setup for Probability Sampling. Inference in Finite Population Sampling. The Horvitz--Thompson Estimator. Simple Random and Allied Sampling Designs. Uses of Auxiliary Size Measures in Survey Sampling: Strategies Based on Probability Proportional to Size Schemes of Sampling. Uses of Auxiliary Size Measures in Survey Sampling: Ratio and Regression Methods of Estimation. Cluster Sampling Designs. Systematic Sampling Designs. Stratified Sampling Designs. Superpopulation Approach to Inference in Finite Population Sampling. Randomized Response: A Data--Gathering Tool for Sensitive Characteristics. Special Topics: Small Area Estimation, Nonresponse Problems, and Resampling Techniques. Author Index. Subject Index.

Creating a System of School Process Indicators

Abstract: A system of school process indicators is needed to provide descriptions of educational opportunity, to monitor reform, and to explain student outputs. Several conceptual and technical problems must first be overcome. A model of school processes is offered against which problems of definition, measurement, and sampling are identified. Using criteria of importance, validity, and cost, a recommendation is made for an initial system of school process indicators. The recommendation illustrates the analytic framework and is meant to begin a conversation.

Stratified adaptive cluster sampling

Abstract: SUMMARY Stratified adaptive cluster sampling refers to designs in which, following an initial stratified sample, additional units are added to the sample from the neighbourhood of any selected unit with an observed value that satisfies a condition of interest. If any of the added units in turn satisfies the condition, still more units are added to the sample. Estimation of the population mean or total with the stratified adaptive cluster designs is complicated by the possibility that a selection in one stratum may result in the addition of units from other strata to the sample, so that observations in separate strata are not independent. Since conventional estimators such as the stratified sample mean are biased with the adaptive designs of this paper, several types of estimators are developed which are unbiased for the population mean or total with stratified adaptive cluster sampling.

Vertical distribution of fish larvae in the Great Barrier Reef Lagoon, Australia

Abstract: The vertical distribution of shorefish — primarily reef fish — larvae in the upper 20 m in relatively shallow (<30 m) waters of the Great Barrier Reef Lagoon near Lizard Island was investigated from 27 February to 7 March 1983 during both day and night Four strata were sampled by neuston net and opening/closing bongo net: neuston (0 to 01 m), upper (0 to 6 m), middle (6 to 13 m), and deep (13 to 20 m) Taxon-specific patterns of vertical distribution which changed little ontogenetically, were found for the 50 taxa (in 24 families) analysed Vertical distribution was highly structured during the day, and with few exceptions was nearly unstructured at night Most taxa had highest concentrations deep in the water column during the day, but in any given stratum some taxa had highest concentrations Day/night changes in pattern apparently were due to randomization or spread, rather than active migration Related taxa had similar patterns Similarity analysis including 211 taxa produced three groupings of samples: day neuston; day upper/middle; and day deep plus all night samples The sampling strategy of using drogues to tag water parcels for subsequent resampling was compared with one of sampling at a fixed point The drogue strategy was not superior to the fixed-point strategy as measured by dissimilarity indices, but this may differ among strata

How geostatistics can help you

Abstract: . Geostatistics is basically a technology for estimating the local values of properties that vary in space from sample data. Research and development in the last 15 years has shown it to be eminently suited for soil and ripe for application in soil survey and land management. The basic technique, ordinary kriging, provides unbiased estimates with minimum and known variance. Data for related variables can be incorporated to improve estimates using cokriging. By more elaborate analysis using disjunctive kriging the probabilities of deficiency and excess can be estimated to aid decision. The variogram is crucial in all geostatistics; it must be estimated reliably from sufficient data at a sensible scale and modelled properly. Once obtained it can be used not only in the estimation itself but also to choose additional sampling sites, improve a monitoring network or design an optimal sampling scheme for a survey. It may also be used to control a multivariate classification so that the resulting classes are not too fragmented spatially to manage.

Real-time sampling electronics for double modulation experiments with Fourier transform infrared spectrometers

Abstract: A novel synchronous real‐time analog sampling method for obtaining the sum and difference interferograms in double modulation Fourier transform infrared absorption experiments is described, and the application of this sampling methodology to polarization‐modulation FTIR measurements of thin films at metal surfaces is demonstrated. A quadratic approximation of the background signal is used to calculate the difference interferogram. The demodulation of a test waveform with the real‐time sampling electronics reveals how the bandwidth limitations of previous double modulation experiments on FTIR interferometers that employed lock‐in amplifiers have been eliminated.