Lform: Hypothesis matrix generated by expressions
In carEx: Supplemental and Experimental Functions

Description Usage Arguments Details Value See Also Examples

Creates an L matrix using expressions evaluated in data for each column of the L matrix

1	Lform(fit, form, data = getData(fit))

`fit`	a fitted model with a `getFix` method.
`form`	formulas (expressions) to evaluate (see Details).
`data`	the data frame in which expressions are evaluated.

If Lform is called with only a fit argument, it outputs code consisting of an expression that would, if used as the form argument to Lform would generate the full model matrix for the linear model.

If Lform is called with two or three arguments, it generates a hypothesis matrix by evaluating the expressions in form in the environment data. The function M is designed to facilitate the generation of blocks of the hypothesis matrix corresponding to main effects or interaction effects of factors.

hypothesis matrix

wald

mod <- lm( income ~ (education + I(education^2) )* type, Prestige)
summary(mod)

# estimate the marginal value of an extra year of education for a
# range of years for each type

years.type <- expand.grid( education = seq(6,18,2), type = levels(Prestige$type))
Lf <- Lform( mod,
   list( 0, 1, 2*education, 0, 0, type =="prof", type =="wc",
      2*education*(type =="prof"), 2*education*(type =="wc")),
   years.type)
Lf
ww <- wald( mod, Lf)
ww
ytderiv <- as.data.frame( ww, se = 2)
head( ytderiv )
if (require("lattice")){
   xyplot(coef ~ education, ytderiv, groups = type, type = 'l',
           auto.key = list(columns = 3, lines = TRUE, points = FALSE))
   }