# yates

##### Population prediction

Compute population marginal means (PMM) from a model fit, for a chosen population and statistic.

##### Usage

```
yates(fit, term, population = c("data", "factorial", "sas"),
levels, test = c("global", "trend", "pairwise"), predict = "linear",
options, nsim = 200, method = c("direct", "sgtt"))
```

##### Arguments

- fit
a model fit. Examples using lm, glm, and coxph objects are given in the vignette.

- term
the term from the model whic is to be evaluated. This can be written as a character string or as a formula.

- population
the population to be used for the adjusting variables. User can supply their own data frame or select one of the built in choices. The argument also allows "empirical" and "yates" as aliases for data and factorial, respectively, and ignores case.

- levels
optional, what values for

`term`

should be used.- test
the test for comparing the population predictions.

- predict
what to predict. For a glm model this might be the 'link' or 'response'. For a coxph model it can be linear, risk, or survival. User written functions are allowed.

- options
optional arguments for the prediction method.

- nsim
number of simulations used to compute a variance for the predictions. This is not needed for the linear predictor.

- method
the computational approach for testing equality of the population predictions. Either the direct approach or the algorithm used by the SAS glim procedure for "type 3" tests.

##### Details

The many options and details of this function are best described in a vignette on population prediction.

##### Value

an object of class `yates`

with components of

a data frame with one row for each level of the term, and columns containing the level, the mean population predicted value (mppv) and its standard deviation.

a matrix giving the test statistics

the full variance-covariance matrix of the mppv values

optional: any further summary if the values provided by the prediction method.

##### Examples

```
# NOT RUN {
fit1 <- lm(skips ~ Solder*Opening + Mask, data = solder)
yates(fit1, ~Opening, population = "factorial")
fit2 <- coxph(Surv(time, status) ~ factor(ph.ecog)*sex + age, lung)
yates(fit2, ~ ph.ecog, predict="risk") # hazard ratio
# }
```

*Documentation reproduced from package survival, version 3.1-8, License: LGPL (>= 2)*