emtrends {emmeans} | R Documentation |
The emtrends
function is useful when a fitted model involves a
numerical predictor x interacting with another predictor a
(typically a factor). Such models specify that x has a different trend
depending on a; thus, it may be of interest to estimate and compare
those trends. Analogous to the emmeans
setting, we construct a
reference grid of these predicted trends, and then possibly average them over
some of the predictors in the grid.
emtrends(model, specs, var, delta.var = 0.01 * rng, data, transform = c("none", "response"), ...)
model |
A supported model object (not a reference grid) |
specs |
Specifications for what marginal trends are desired – as in
|
var |
Character value giving the name of a variable with respect to
which a difference quotient of the linear predictors is computed. In order
for this to be useful, |
delta.var |
The value of h to use in forming the difference
quotient (f(x+h) - f(x))/h. Changing it (especially changing its
sign) may be necessary to avoid numerical problems such as logs of negative
numbers. The default value is 1/100 of the range of |
data |
As in |
transform |
If |
... |
Additional arguments passed to other methods or to
|
An emmGrid
or emm_list
object, according to specs
.
See emmeans
for more details on when a list is returned.
Instead of a single predictor, the user may specify some monotone function of
one variable, e.g., var = "log(dose)"
. If so, the chain rule is
applied. Note that, in this example, if model
contains
log(dose)
as a predictor, we will be comparing the slopes estimated by
that model, whereas specifying var = "dose"
would perform a
transformation of those slopes, making the predicted trends vary depending on
dose
.
link{emmeans}
, ref_grid
fiber.lm <- lm(strength ~ diameter*machine, data=fiber) # Obtain slopes for each machine ... ( fiber.emt <- emtrends(fiber.lm, "machine", var = "diameter") ) # ... and pairwise comparisons thereof pairs(fiber.emt) # Suppose we want trends relative to sqrt(diameter)... emtrends(fiber.lm, ~ machine | diameter, var = "sqrt(diameter)", at = list(diameter = c(20, 30)))