# pmtree

From model4you v0.9-5
by Heidi Seibold

##### Compute model-based tree from model.

Input a parametric model and get a model-based tree.

##### Usage

```
pmtree(model, data = NULL, zformula = ~., control = ctree_control(),
coeffun = coef, ...)
```

##### Arguments

- model
a model object. The model can be a parametric model with a binary covariate.

- data
data. If NULL (default) the data from the model object are used.

- zformula
formula describing which variable should be used for partitioning. Default is to use all variables in data that are not in the model (i.e.

`~ .`

).- control
control parameters, see

`ctree_control`

.- coeffun
function that takes the model object and returns the coefficients. Useful when

`coef()`

does not return all coefficients (e.g.`survreg`

).- ...
additional parameters passed on to model fit such as weights.

##### Details

Sometimes the number of participant in each treatment group needs to
be of a certain size. This can be accomplished by setting `control$converged`

.
See example below.

##### Value

ctree object

##### Examples

```
# NOT RUN {
if(require("TH.data") & require("survival")) {
## base model
bmod <- survreg(Surv(time, cens) ~ horTh, data = GBSG2, model = TRUE)
survreg_plot(bmod)
## partitioned model
tr <- pmtree(bmod)
plot(tr, terminal_panel = node_pmterminal(tr, plotfun = survreg_plot,
confint = TRUE))
summary(tr)
summary(tr, node = 1:2)
logLik(bmod)
logLik(tr)
## Sometimes the number of participant in each treatment group needs to
## be of a certain size. This can be accomplished using converged
## Each treatment group should have more than 33 observations
ctrl <- ctree_control(lookahead = TRUE)
ctrl$converged <- function(mod, data, subset) {
all(table(data$horTh[subset]) > 33)
}
tr2 <- pmtree(bmod, control = ctrl)
plot(tr2, terminal_panel = node_pmterminal(tr, plotfun = survreg_plot,
confint = TRUE))
summary(tr2[[5]]$data$horTh)
}
if(require("psychotools")) {
data("MathExam14W", package = "psychotools")
## scale points achieved to [0, 100] percent
MathExam14W$tests <- 100 * MathExam14W$tests/26
MathExam14W$pcorrect <- 100 * MathExam14W$nsolved/13
## select variables to be used
MathExam <- MathExam14W[ , c("pcorrect", "group", "tests", "study",
"attempt", "semester", "gender")]
## compute base model
bmod_math <- lm(pcorrect ~ group, data = MathExam)
lm_plot(bmod_math, densest = TRUE)
## compute tree
(tr_math <- pmtree(bmod_math, control = ctree_control(maxdepth = 2)))
plot(tr_math, terminal_panel = node_pmterminal(tr_math, plotfun = lm_plot,
confint = FALSE))
plot(tr_math, terminal_panel = node_pmterminal(tr_math, plotfun = lm_plot,
densest = TRUE,
confint = TRUE))
## predict
newdat <- MathExam[1:5, ]
# terminal nodes
(nodes <- predict(tr_math, type = "node", newdata = newdat))
# response
(pr <- predict(tr_math, type = "pass", newdata = newdat))
# response including confidence intervals, see ?predict.lm
(pr1 <- predict(tr_math, type = "pass", newdata = newdat,
predict_args = list(interval = "confidence")))
}
# }
```

*Documentation reproduced from package model4you, version 0.9-5, License: GPL-2 | GPL-3*

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