Quantile Regression: Non-insect Relative Abundance vs. Percent Sands and Fines for Minnesota Streams
- Analysis: Quantile regression
- Independent variable: Percentage (%), sand and fines
- Dependent variable: Non-insect abundance/m²
- Classification variables: Ecoregion class - dummy variable = 0 if the ecoregions are 46, 47, or 51 and dummy variable = 1 if the ecoregions are 50 or 52
- Key: symbols = observations, solid line = mean line, dashed line = 95% prediction limit. Black lines and symbols: Ecoregions 46, 47 and 51, blue lines and symbols: Ecoregions 50 and 52
- Sample size: n = 267
- Ecoregions 50 and 52: Non-insect abundance = 67.00 + 1.17(% sand & fines)
- Ecoregions 46, 47 and 51: Non-insect abundance = 82.58 + 3.28(% sand & fines)
- Date: 6 October, 2006
|% Sand & fines||3.284||14.49||0.0001|
|% Sand & fines x Ecoregion class||-2.114||5.21||0.022|
- Model generated using SAS Proc QUANTREG with the smoothing algorithm. The Wald test statistic was used to test the linear null hypothesis, H0: slope=0, for all independent variables (i.e., ecoregion class, % sand & fines, and ecoregion class x % sand & fines.)
- The ecoregions were aggregated into two classes because a preliminary ANOVA indicated that the base material for bedded sediments, % coarse substrates, was significantly greater in Ecoregions 50 and 52 than in Ecoregions 46, 47, and 51. Percent coarse substrates, however, did not significantly differ within either group.
- Replicate visits to a site were excluded from the data set.
- Agency: Minnesota Pollution Control Agency , St. Paul, Minnesota
- Location: Minnesota - analyses restricted to wadeable sites (52 km² < watershed area < 523 km²) from the five ecoregions indicated below.
- Omernik Level III Ecoregions examined include: 46 (Northern Glaciated Plains), 47 (Western Corn Belt Plains), 50 (Northern Lakes and Forests), 51 (North Central Hardwoods), and 52 (Driftless Area).
- Data collected 1996 through 2004.
- Sampling protocols:
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Michael B. Griffith, email@example.com, (513) 569-7034