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R functions AOV contrast doc - 5:26 PM File =...

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4/9/03 5:26 PM File = E:\r\fns\aov.contrast doc.doc 1 John Miyamoto Department of Psychology, Box 351525, University of Washington, Seattle, WA 98195 Email: [email protected] April 9, 2003 Documentation for the 'aov.contrast' Function This documentation has four sections. Section I presents documentation in the standard R-Help format. It is probably more useful for people who are experienced users of R. Section II has a more discursive explanation of the aov.contrast function that is probably more useful to more inexperienced users of R. Section III has examples that use 'aov.contrast' in the context of an analysis of covariance. Section IV shows the R code for the 'aov.contrast' function. ---------------------------------------------------------------------- Section I: R documentation for the 'aov.contrast' function Description Computes t-tests, confidence intervals, and other statistics for user-defined contrasts (linear combinations of cell means) in a between-subjects analysis of variance (completely randomized design). Usage aov.contrast <- function(lm.input, margin=1, contrast.list, strata=NA, Confidence.Level = .95, var.equal=TRUE, show.cellcode=TRUE, p.digits=6) Arguments lm.input A 'lm' or 'aov' object, i.e., the output of a call to 'lm' or 'aov'. margin A vector of positive integers that indicate the factor or factors over whose levels the contrast is defined. The factors are listed in the same order as in the 'formula' argument of the call to 'aov'. For example, if the 'Y ~ A1*A2*A3' is the formula in the call to 'aov', then 'margin=3' indicates that the contrast coefficients apply to the levels of the 'A3' factor. contrast.list A list of numeric vectors. Each vector indicates the contrast coefficients for the marginal means specified by 'margin'. All vectors must have the same length as the number of marginal means determined by 'margin'. strata If 'strata' is non-missing, it must be a vector of integers indicating the factor or factors that play the role of strata. Each contrast is computed within every fixed level of the stratifying factors. Confidence.Level Level of confidence for the confidence intervals. var.equal If var.equal = TRUE if and only if homogeneity of variance is assumed in the test of the contrast. The default is var.equal = TRUE. show.cellcode When margin specifies more than one factor, e.g., 'margin = c(2, 3)', the contrast coefficients define a linear combination with respect to all combinations of factors 2 and 3. If factor 2 has k levels and factor 3 has m levels, there are k*m combinations of levels. If 'show.cellcode = TRUE', then the output displays the correspondence between the sequence of coefficients specified through 'contrast.list' and the k*m levels of factors 2 and 3.
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