R: Summarize an Analysis of Variance Model

summary.aov {stats} | R Documentation

## Summarize an Analysis of Variance Model

### Description

Summarize an analysis of variance model.

### Usage

    ## S3 method for class 'aov'
    summary(object, intercept = FALSE, split,
            expand.split = TRUE, keep.zero.df = TRUE, ...)

    ## S3 method for class 'aovlist'
    summary(object, ...)

### Arguments

`object` | An object of class `"aov"` or `"aovlist"`.
`intercept` | logical: should intercept terms be included?
`split` | an optional named list, with names corresponding to terms in the model. Each component is itself a list with integer components giving contrasts whose contributions are to be summed.
`expand.split` | logical: should the split apply also to interactions involving the factor?
`keep.zero.df` | logical: should terms with no degrees of freedom be included?
`...` | Arguments to be passed to or from other methods, for `summary.aovlist` including those for `summary.aov`.

### Value

An object of class `c("summary.aov", "listof")` or `"summary.aovlist"` respectively.

For fits with a single stratum the result will be a list of ANOVA tables, one for each response (even if there is only one response): the tables are of class `"anova"` inheriting from class `"data.frame"`. They have columns `"Df"`, `"Sum Sq"`, `"Mean Sq"`, as well as `"F value"` and `"Pr(>F)"` if there are non-zero residual degrees of freedom. There is a row for each term in the model, plus one for `"Residuals"` if there are any.

For multistratum fits the return value is a list of such summaries, one for each stratum.

### Note

The use of `expand.split = TRUE` is little tested: it is always possible to set it to `FALSE` and specify exactly all the splits required.

### See Also

`aov`, `summary`, `model.tables`, `TukeyHSD`

### Examples

    ## For a simple example see example(aov)

    # Cochran and Cox (1957, p.164)
    # 3x3 factorial with ordered factors, each is average of 12.
    CC <- data.frame(
        y = c(449, 413, 326, 409, 358, 291, 341, 278, 312)/12,
        P = ordered(gl(3, 3)), N = ordered(gl(3, 1, 9))
    )
    CC.aov <- aov(y ~ N * P, data = CC , weights = rep(12, 9))
    summary(CC.aov)

    # Split both main effects into linear and quadratic parts.
    summary(CC.aov, split = list(N = list(L = 1, Q = 2),
                                 P = list(L = 1, Q = 2)))

    # Split only the interaction
    summary(CC.aov, split = list("N:P" = list(L.L = 1, Q = 2:4)))

    # split on just one var
    summary(CC.aov, split = list(P = list(lin = 1, quad = 2)))
    summary(CC.aov, split = list(P = list(lin = 1, quad = 2)),
            expand.split=FALSE)

[Package stats version 2.15.1 Index]