Surface Collection Sample Fraction
Compute area inclusion fractions and stratified expansion from sampled counts, assuming representative selection within each stratum; unequal strata are not replaced by a single uniform inclusion rate.
Description
Stratified surface sampling can use a different sampled fraction in each area.
Stratified surface sampling can use a different sampled fraction in each area. Expanding each stratum's count separately preserves those unequal inclusion rates.1
Compute area inclusion fractions and stratified expansion from sampled counts, assuming representative selection within each stratum; unequal strata are not replaced by a single uniform inclusion rate.
When to use Surface Collection Sample Fraction
Use this tool to compute area inclusion fractions and stratified expansion from sampled counts, assuming representative selection within each stratum; unequal strata are not replaced by a single uniform inclusion rate.
Prepare the artifact, site or survey measurements and any independently established calibration or model choices. Keep paired observations aligned and confirm units and coordinate conventions.
How to use Surface Collection Sample Fraction and understand its results
- Prepare the artifact, site or survey measurements and any independently established calibration or model choices. Keep paired observations aligned and confirm units and coordinate conventions.
- Enter stratumTotalAreasM2, stratumCollectedAreasM2, stratumSherdCounts using the field table and calculation rules, then run the tool.
- Read stratumSampleFractions, overallAreaSampleFraction, stratifiedExpandedSherdCount. The explanation below defines the units, signs, ordering and any flags or placeholder values.
- If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.
| Input field | Meaning | Value type; see rules below | Requirement |
|---|---|---|---|
| stratumTotalAreasM2 | Stratum total areas m2 | list of number | Required |
| stratumCollectedAreasM2 | Stratum collected areas m2 | list of number | Required |
| stratumSherdCounts | Stratum sherd counts | list of number | Required |
Pair positive total and collected areas in m² and nonnegative integer collected sherd counts. Collected area cannot exceed its stratum total. Return each sampling fraction, the pooled sampled-area fraction and the sum of separately expanded stratum counts.
Paired lists must be nonempty and have equal lengths.
fraction_i = sampledArea_i/totalArea_i; expandedCount = Σ count_i/fraction_i Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| stratumSampleFractions | Stratum sample fractions | list of number |
| overallAreaSampleFraction | Overall area sample fraction | number |
| stratifiedExpandedSherdCount | Stratified expanded sherd count | number |
{
"input": {
"stratumTotalAreasM2": [
100,
200
],
"stratumCollectedAreasM2": [
10,
40
],
"stratumSherdCounts": [
5,
10
]
},
"output": {
"stratumSampleFractions": [
0.1,
0.2
],
"overallAreaSampleFraction": 0.16666666666666666,
"stratifiedExpandedSherdCount": 100
}
}Limitations and assumptions
Expansion assumes representative sampling within each stratum. Detection loss and survey uncertainty are not corrected, and the estimate does not establish an observed site-wide census.
Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Numeric lists are limited to 100,000 entries; the rules above may require smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.
Alternative or Complementary methods
Use Transect Sherd Density: Aggregate strip-collected sherd density with caller detection probabilities, using physical exposure areas rather than averaging unequal transects; detection correction is a model, not total site inventory. For a complementary task, use NISP Specimen Count By Taxa Tool: Tabulate one taxon assignment per observed specimen while retaining explicitly unassigned records; fragmentation and element counts do not convert NISP to individuals.
References
-
Surface Collection Sample Fraction — tool.io
Similar or alternative tools
- Transect Sherd Density
Aggregate strip-collected sherd density with caller detection probabilities, using physical exposure areas rather than averaging unequal transects; detection correction is a model, not total site inventory.
- NISP Specimen Count By Taxa Tool
Tabulate one taxon assignment per observed specimen while retaining explicitly unassigned records; fragmentation and element counts do not convert NISP to individuals.