extend function

Extend a longitudinal model.

This method increases the sample size for a model.

extend(object, along, within, n, values)

Arguments

• object: a fitted model object to extend.
• along: the name of an explanatory variable. This variable will have its number of levels extended.
• within: names of grouping variables, separated by "+" or ",". Each combination of groups will be extended to n rows.
• n: number of levels: the levels of the explanatory variable will be replaced by 1,2,3,..,n for a continuous variable or a,b,c,...,n for a factor.
• values: alternatively, you can specify a new set of levels for the explanatory variable.

Returns

A copy of object suitable for doSim with an extended dataset attached as an attribute named newData.

Details

extend takes "slices" through the data for each unique value of the extended variable. An extended dataset is built from n slices, with slices duplicated if necessary.

Examples

fm <- lmer(y ~ x + (1|g), data=simdata)
nrow(example)
fmx1 <- extend(fm, along="x", n=20)
nrow(getData(fmx1))
fmx2 <- extend(fm, along="x", values=c(1,2,4,8,16))
nrow(getData(fmx2))