Quantile Regression: Number of Salmonids vs. Metal Toxicity Units for Colorado Streams
Plot
- Analysis: Quantile regression
- Independent variable: Metal Toxicity Units
- Dependent variable: Number of salmonids
- Key: dot=observation; line= 90th quantile
- Sample size: n = 30
Model
- Number of salmonids = 153.3 - 111.364*(Metal Toxicity Units)
- 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
- 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.
- Analysis for sites classified as pH neutral, but with strong AMD input.
- Metal Toxicity Units (TU) were calculated as sum of the ratios of each measured metal concentration with the criterion for that metal.
- Replicate visits to a site were not excluded from the data set.
Data Origin
- Agency: U.S. Environmental Protection Agency
- Program: Environmental Monitoring and Assessment Program (EMAP)
- Project: Colorado Metals Belt Stream Assessment (EPA Region 8)
- Filenames: Files benmet, fishmet and chem downloaded from the Surface Waters Information Management (S.W.I.M.S.) database web site
Sampling Design
- Data collected 1994 through 1995.
- Analyzed metals and metalloids: aluminum, arsenic, cadmium, chromium, copper, iron, manganese, nickel, lead, selenium, silver, zinc.
- 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.