Download pdf guide - VSN International

118 9 Commands for analysis of variancethe marginal test for A will show the effect of adding A to a model containing onlyBlocks, while the conditional test will show the effect of adding A to a model containingBlocks and B. (The terms A and B are marginal to A.B.)Like A2WAY, AUNBALANCED forms tables of means using the PREDICT directive andagain has options COMBINATIONS and ADJUSTMENT to control how this is done. ThePSE option controls the types of standard errors that are produced to accompany thetables of means, with settings: differences for a summary of the standard errors fordifferences between pairs of means, alldifferences for standard errors for differencesbetween all pairs of means, lsd for a summary of the least significant differencesbetween pairs of means, alllsd for all the least significant differences between pairs ofmeans, and means for standard errors of the means (relevant for comparing them withzero). The default is differences. The NOMESSAGE option allows various warningmessages (produced by the FIT directive) to be suppressed, and the PLOT option allowsvarious residual plots to be requested: fittedvalues for a plot of residuals againstfitted values, normal for a Normal plot, halfnormal for a half Normal plot, andhistogram for a histogram of residuals.Procedure AUDISPLAY is used to produce further output for an unbalanced design. Ithas options PRINT, FPROBABILITY, COMBINATIONS, ADJUSTMENT, PSE andLSDLEVEL like those of AUNBALANCED, except that no screening tests are available.The menus described in Chapter 8 use the REML directive. Before using REML we firstneed to define the model that is to be fitted in the analysis. For straightforward linearmixed models, the only directive that needs to be specified is VCOMPONENTS. The FIXEDoption specifies a model formula defining the fixed model terms to be fitted, and theRANDOM parameter specifies another model formula defining the random terms. There aretwo other parameters. INITIAL provides initial values for the estimation of each variancecomponent. These are supplied as the ratio of the component to the residual variance, butthe default value of one is usually satisfactory. The CONSTRAINT parameter can be usedto indicate whether each variance component is to be constrained in any way. The defaultsetting, none, leaves them unconstrained. The positive setting forces a variancecomponent to be kept positive, the fixrelative fixes the relative value of thecomponent to be equal to that specified by the INITIAL parameter, and thefixabsolute setting fixes it to the absolute value specified by INITIAL. TheFACTORIAL option sets a limit on the number of factors and variates allowed in eachfixed term (default 3); any term containing more than that number is deleted from themodel.Usually, only FIXED and RANDOM need to be set. For example, the statement belowdefines the models for the split-plot example in Section 7.1.VCOMPONENTS [FIXED=variety*nitrogen] \RANDOM=blocks/wplots/subplotsOnce the models have been defined, the REML directive can be used to perform theanalysis. The first parameter of REML specifies the y-variate to be analysed. The PRINToption is set to a list of strings to select the output to be printed. These are similar to thecheck boxes of the Further Output menu. The most commonly used settings are:modeldescription of model fitted,componentsestimates of variance components and estimatedparameters of covariance models,effectsestimates of parameters in the fixed and random