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Strategies for Allocation of Sample Sites
Several strategies are available for the allocation of sample sites in space and time to meet the survey objectives.
Panels and Rotating Basins - Examples
- A collection of sites that will have the same revisit schedule over time
- Basic design is single panel
- 5-year rotating panel: panel 1 sites visited in years 1, 6, 11, etc.; panel 2 in years 2, 7, 12, etc; etc.
- More complexity possible to balance priority of status estimation versus trend estimation
Nested Subsamples - Example
Primarily useful when all measurements are not made at all sites. For example, water quality observations maybe made at all sites, while sediment chemistry and benthic observations are made at a subsample of those sites, while sediment toxicity and tissue contaminant determinations are made at only a subsample of those sites. Thus nested subsamples would have:
- sites with water quality data
- sites with water quality, sediment chemistry, and benthic data
- sites with water quality, sediment chemistry, benthic, sediment toxicity and tissue contaminant data
Multi-Density - Example
- Important and widely used strategy
- Supports unequal probability strategies
- Subpopulations (categories) within Target Population with unequal weights (Inclusion Probabilities or Probability of Selection)
Intensification
- Design strategy that supports special interest areas
- Primary objectives achievable w/ or w/o completion of special interest area survey
- Supports correct analysis of combined larger area and special interest area data
- Primarily used when uncertain of special interest area survey completion
Over-Sample
- Design Adjustment for Sample Site Issues
- Expected non-target sites
- Landowner access denial sites
- Physically inaccessible sites
- Oregon State Rates after Surveys