Sampling for Decision Making

Overview of the course

Sampling is a key component of data gathering. Forty years of experience has shown that many of the textbook schemes are not practical in reality, This results in incorrect assertions, biases and lack of precision. The course is supported by numerous first-hand examples ranging across agriculture, environmental sampling, monitoring and quarantine sampling.

The course is not meant to take the place of a text on the statistical theory of sampling. This can be found in classical texts such as that of Cochran WG (1977). It is more a bridge between the theory and field reality.

The topics covered include:

Introduction
  • Why we need samples
  • What is the purpose of the sampling?
Defining the problem
  • What is the population (surprisingly difficult to define)
  • What are sampling units
Decision rules
Precision and accuracy
  • Examples of biased sampling
  • How to avoid bias in your samples
  • Sampling plants in the field
Common sampling schemes
  • Simple random sampling
  • Stratified and Cluster Sampling – is it worth it?
  • Systematic sampling
Model based sampling
  • Kriging
  • Fitting dispersion models
Data acquisition
  • How to reduce sampling costs with composite samples
  • Sample labelling
  • Chain of custody (including biosecurity)
How many samples
Monitoring versus sampling
Estimating confidence intervals
  • Non-normal distributions
  • Transformations
Increasing precision
  • Using prior knowledge
  • Use of covariates
Questions without notice

The Presenter

Dr Ray Correll is trained ecologist and statistician with extensive experience in sampling. His experience covers many areas of biological and environmental sampling especially as a component of risk assessments. He has advised on many projects including assessing safety of electrical distribution grids, phytotoxins in farm produce and quarantine issues.

Ray places emphasis on practical issues of sampling and believes that a statistician always learns from field visits.

Contact details:

Dr Ray Correll
Rho Environmetrics
PO Box 366 Highgate South Australia 5063
E-mail rho.environmetrics@bigpond.com

Further reading

  • Buckland ST, Anderson DR, Burnham ΚΡ and Laake JL (1993) Distance sampling: Estimating abundance of biological populations London: Chapman and Hall
  • Cochran WG (1963) Sampling techniques 2nd Edition Wiley International, NY
  • Cochran WG (1977) Sampling techniques 3rd Edition Wiley International, NY
  • Correll, R.L. (2001).  The use of composite sampling in contaminated sites - a case study.  Environmental and Ecological Statistics 8 (3) 185-200.
  • de Gruijter J, Brus D, Bierkens M and Knotters M (2006) Sampling for natural resource monitoring Springer, Berlin
  • Codex General guidelines on sampling. CODEX CAC/GL 50-2004.
  • Codex General standard for contaminants and toxins in food and feed. CODEX STAN 193-1995
  • Lohr S. (2010) Sampling: Design and analysis. 2nd Edition Brooks/Cole, Boston.
  • Maher C and Burke T (1991) Informed decision making Longman-Cheshire, Melbourne
  • Moser CA and Kalton G (1973) Survey methods in social investigation Heinemann Education Books, London
  • Recommended methods of sampling for the determination of pesticide residues for compliance with mrls. CAC/GL 33-1999

 

 

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