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Conditional Probability Analysis: EPT Taxa Richness < 9 vs. Percent Fines for Mid-Atlantic Highland Streams

CPA for Mid-Atlantic Highlands Streams


  1. Analysis: Conditional probability analysis
  2. Independent variable: Percent fines in substrate ( < 0.06 mm, silt/clay)
  3. Dependent variable: Probability of unacceptable condition for EPT taxa richness at < 9
  4. Key: symbols = observations, solid line = nonlinear curve fit to the observations with a change in slope, dashed line = 95% Confidence Intervals
  5. Sample size: N = 99


  1. Conditional probability analysis does not produce a model equation. Rather, it plots the probabilities of observing the stated impairment (i.e. item 3 in the list above) over a stressor intensity gradient.
  2. Date: 8 November 2006

Data Analysis

  1. Program: S-Plus Version 7.0, user written scripts, variable weighting for site data

Data Origin

  1. Agency: U.S. Environmental Protection Agency
  2. Program: Environmental Monitoring and Assessment Program (EMAP)
  3. Project: EMAP Surface Waters, Mid-Atlantic Streams Assessment
  4. Location: Mid-Atlantic region
  5. Environmental Monitoring and Assessment Program (EMAP) data and metadata.

Sampling Design

  1. Sample collected using the EMAP probability design in April through June and July through September of the years 1993 through 1996.
  2. Multi-habitat sample of benthos assemblage and substrate taken during spring low-flow, modified kicknet with 595 micron mesh.
  3. Lazorchak, J.M., Klemm, D.J., and Peck D.V. (editors). 1998. Environmental Monitoring and Assessment Program- Surface Waters: Field Operations and Methods for Measuring the Ecological Condition of Wadeable Streams. EPA/620/R-94/004F.
  4. U.S. Environmental Protection Agency, Washington, D.C. Catalog Documentation for EMAP Surface Waters 1993-96 Mid-Atlantic Streams Data.


John F. Paul,, (919) 541-3160

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