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CADDIS Volume 3

Quantile Regression: Number of Salmonids vs. Metal Toxicity Units for Colorado Streams


  1. Analysis: Quantile regression
  2. Independent variable: Metal Toxicity Units
  3. Dependent variable: Number of salmonids
  4. Key: dot=observation; line= 90th quantile
  5. Sample size: n = 30


  1. Number of salmonids = 153.3 - 111.364*(Metal Toxicity Units)
  2. Date: 12 November, 2006
Variable Estimate Lower CL Upper CL Test Type Statistic p
Intercept 153.300 -178.102 484.702 T value 0.948  
Metal Toxicity Units -111.364 -656.511 433.782 T value -0.418 0.679
WALD       Chi2 0.175 0.676
Likelihood Ratio       Chi2 6.494 0.011

Data Analysis

  1. Model generated using SAS Proc QUANTREG with the smoothing algorithm. The WALD and Likelihood test statistics were used to test the linear null hypothesis, H0: slope=0.
  2. Analysis for sites classified as pH neutral, but with strong AMD input.
  3. Metal Toxicity Units (TU) were calculated as sum of the ratios of each measured metal concentration with the criterion for that metal.
  4. Replicate visits to a site were not excluded from the data set.

Data Origin

  1. Agency: U.S. Environmental Protection Agency
  2. Program: Environmental Monitoring and Assessment Program (EMAP)
  3. Project: Colorado Metals Belt Stream Assessment (EPA Region 8)
  4. Filenames: Files benmet, fishmet and chem downloaded from the Surface Waters Information Management (S.W.I.M.S.) database web site

Sampling Design

  1. Data collected 1994 through 1995.
  2. Analyzed metals and metalloids: aluminum, arsenic, cadmium, chromium, copper, iron, manganese, nickel, lead, selenium, silver, zinc.
  3. A description of the sampling methods may be found in the EMAP West Methods Manual for Streams found on the S.W.I.M.S. database web site.

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