Representative data read from a plot on runoff sediment concentration for plots
ID: 3246139 • Letter: R
Question
Representative data read from a plot on runoff sediment concentration for plots with varying amounts of grazing damage, measured by the percentage of bare ground in the plot, are given for steeply sloped plots. Steeply Sloped Plots Bare ground (%) 8 8 16 24 32 40 32 48 56 64 56 Concentration 90 225 270 540 450 450 810 720 990 1080 900 (a) Using the data for steeply sloped plots, find the equation of the least-squares line for predicting y runoff sediment concentration using x = percentage of bare ground. (Give the answer to two decimal places.) y = Incorrect: Your answer is incorrect. (b) What would you predict runoff sediment concentration to be for a steeply sloped plot with 16% bare ground? (Round your answer to the nearest whole number.)
Explanation / Answer
using minitab
Regression Analysis: concentration versus bareground%
Analysis of Variance
Source DF Adj SS Adj MS F-Value P-Value
Regression 1 924667 924667 50.73 0.000
bareground% 1 924667 924667 50.73 0.000
Error 9 164046 18227
Lack-of-Fit 6 86084 14347 0.55 0.755
Pure Error 3 77963 25988
Total 10 1088714
Model Summary
S R-sq R-sq(adj) R-sq(pred)
135.009 84.93% 83.26% 80.50%
Coefficients
Term Coef SE Coef T-Value P-Value VIF
Constant 53.9 86.0 0.63 0.546
bareground% 15.45 2.17 7.12 0.000 1.00
Regression Equation
concentration = 53.9 + 15.45 bareground%
Fits and Diagnostics for Unusual Observations
Std
Obs concentration Fit Resid Resid
7 810.0 548.2 261.8 2.04 R
R Large residual
a) concentration = 53.9 + 15.45 bareground%
b) substitute bareground =16
concentration =53.9+15.45*16
=301.100
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