On Wed, 1 May 2013, Elaine Kuo wrote:
Hello,
I am work with a linear regression model:
y=ax+b with the function of lm.
y= observed migration distance of butterflies
x= predicted migration distance of butterflies
Usually the result will show
if the linear term a is significantly different from zero based on the
p-value.
Now I would like to test if the linear term is significantly different from
one.
(because I want to know if the regression line (y=ax+b) is significantly
from the line with the linear term =1 and the intercept =0)
In addition to the solutions suggested by Paul and Thomas, you could use
linearHypothesis() from the "car" package. A (non-sensical) example using
the cars dataset is:
m <- lm(dist ~ speed, data = cars)
linearHypothesis(m, c("(Intercept) = 0", "speed = 1"))
The output is equivalent to the anova() for the offset model that Thomas
suggested:
m0 <- lm(dist ~ 0 + offset(1 * speed), data = cars)
anova(m0, m)
Please kindly advise if it is possible
to adjust some default parameters in the function to achieve the goal.
Thank you.
Elaine
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