Scientific Investigations Report 2008–5025
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5025
Table 2. Regression coefficients and individual p-values of independent variables for the two logistic regression models with and without hydrogeomorphic regions that were significantly related with nitrate concentrations greater than 2 milligrams per liter in ground water in Washington.
[Abbreviations: -, no data; <, less than.]
| Independent variable | With hydrogeomorphic region | Without hydrogeomorphic region | Regression coefficients |
p-values | Regression coefficients |
p-values |
|---|---|---|---|---|---|
| Logistic regression constant | 1.6132 | <0.0001 | 1.3857 | <0.0001 | |
| Well depth, in feet | -.00436 | <.0001 | -.00388 | <.0001 | |
| Average annual precipitation, in inches | -.0252 | <.0001 | -.026 | <.0001 | |
| Percentage of agricultural land within a 4-kilometer buffer | .0276 | <.0001 | .0275 | <.0001 | |
| 2000 population density | .000064 | <.0001 | .00007 | <.0001 | |
| Soil drainage | -.5796 | <.0001 | -.5554 | <.0001 | |
| Hydrogeomorphic region | |||||
| Eastern Washington basin fill | -.3349 | .0011 | – | – | |
| Columbia basalts | .1583 | .128 | – | – | |
| Bedrock | -.4621 | <.0001 | – | – | |
| Willamette basin | .0337 | .7963 | – | – | |
| Western Washington basin fill | -.7302 | <.0001 | – | – | |
U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/sir/2008/5025
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