Target Population - Frame - Sample - Estimates

Target population denotes the ecological resource about which estimates are needed

Defined conceptually using written text
Must be sufficiently specific so that it is clear if an aquatic resource is included or not.
Must define what are the elements of the target population. Elements may be

Sampling Frame is a physical representation of the target population

It consists of sample units that are potential members of the sample
Extent (size) of the frame is obtained by summation
Sample Frames almost always are not exact representations of the target population

Sample Frame may not include some Target Population elements: Undercoverage
Sample Frame may contain non-target elements, e.g., mis-identified sample units: Overcoverage
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A subset of the Sample Frame sample units are selected for sampling: the sample

One design: Generalized Random Tessellation Stratified Designs - GRTS
May include stratification, unequal probability selection, panels for surveys over time

Sample Frame overcoverage and sample site field access problems addressed by including an Oversample
Sampling Units are the Sites selected for sampling
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Sampled Population is a conceptual population that is a subset of intersection the Target Population and the Sample Frame

It excludes portion of the Target Population within the Sample Frame that could not be sampled (conceptually) due to access problems, lost samples, or other reasons a sample could not be collected
It doesn't include part of the Sample Frame that is determined to not be elements of the Target Population
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Population Estimates are based on All Sites Evaluated for potential field sampling

Site Evaluation and Field Sampling Categorizing each Sample Site is critical information

Target Sampled -- Site Information Collected
Landowner Denial -- Some landowners deny field crew access
Physical Barrier -- Site can not physically be reached within protocols or for safety reasons
Target Not-Sampled -- Sample lost, field season ended before site could be sampled, and many other reasons
Non-Target -- Site not element of target population

Provides estimate of the Target Population extent if it is not known
Provides estimate of the Sample Frame overcoverage extent, i.e., how much too large is Frame
Provides estimate of percent of Target Population that is expected to have landowners deny access

Population Status estimates based on Target Sampled Sites (e.g., IBI score, non- Impairment)
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Potential Corrections and Assumptions

Non-Target Site Information can be used to determine if Sample Frame should be improved (mis-identified units, extent)
Estimates based on Target Sampled sites apply to the Sampled Population -- with no additional assumptions
Estimates based on Target Sampled sites can apply to the portion of Target Population within the Sample Frame ONLY IF assume that the Access Denied, Target Not-Sampled, etc., sites occurred randomly and independently of site characteristics
Estimates for Target Population NOT ONLY require assumptions above BUT ALSO that portions of Target Population that are not included in the Sample Frame have same characteristics as the Sampled Population
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