This function is a constructor for the
corCompSymm class, representing a compound symmetry structure corresponding to uniform correlation. Objects created using this constructor must later be initialized using the appropriate
corCompSymm(value, form, fixed)
- the correlation between any two correlated observations. Defaults to 0.
- a one sided formula of the form
~ t, or
~ t | g, specifying a time covariate
tand, optionally, a grouping factor
g. When a grouping factor is present in
form, the correlation structure is assumed to apply only to observations within the same grouping level; observations with different grouping levels are assumed to be uncorrelated. Defaults to
~ 1, which corresponds to using the order of the observations in the data as a covariate, and no groups.
- an optional logical value indicating whether the coefficients should be allowed to vary in the optimization, or kept fixed at their initial value. Defaults to
FALSE, in which case the coefficients are allowed to vary.
an object of class
corCompSymm, representing a compound symmetry correlation structure.
Milliken, G. A. and Johnson, D. E. (1992) "Analysis of Messy Data, Volume I: Designed Experiments", Van Nostrand Reinhold.
Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S and S-PLUS", Springer, esp. pp. 233-234.
## covariate is observation order and grouping factor is Subject cs1 <- corCompSymm(0.5, form = ~ 1 | Subject) # Pinheiro and Bates, pp. 222-225 fm1BW.lme <- lme(weight ~ Time * Diet, BodyWeight, random = ~ Time) # p. 223 fm2BW.lme <- update(fm1BW.lme, weights = varPower()) # p. 225 cs1CompSymm <- corCompSymm(value = 0.3, form = ~ 1 | Subject) cs2CompSymm <- corCompSymm(value = 0.3, form = ~ age | Subject) cs1CompSymm <- Initialize(cs1CompSymm, data = Orthodont) corMatrix(cs1CompSymm)
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