VLSD procedure

Prints approximate least significant differences for REML means (R.W. Payne).


Options

PRINT = strings
Controls printed output (means, sed, lsd, df); default lsd

FACTORIAL = scalar
Limit on the number of factors in each term; default 3

LSDLEVEL = scalar
Significance level (%) to use in the calculation of least significant differences; default 5

SAVE = REML save structure
Save structure to provide the table of means; default uses the save structure from the most recent REML


Parameters

TERMS = formula
Treatment terms whose means are to be compared; default * takes the REML fixed model

MEANS = pointer or table
Saves the means for each term

SED = pointer or symmetric matrix
Saves standard errors of differences between means

LSD = pointer or symmetric matrix
Saves approximate least significant differences matrix for the means

DF = pointer or scalar
Saves the degrees of freedom used to calculate the t critical values for the LSDs

DDF = pointer or scalar
Saves the denominator degrees of freedom in the F test for the term


Description

VLSD calculates least significant differences (LSDs) for predicted means of fixed terms in a REML analysis. These are calculated using the approximate numbers of residual degrees of freedom printed by REML in the d.d.f. column in the table of tests for fixed tests (produced by setting option PRINT=wald). The degrees of freedom are relevant for assessing the fixed term as a whole, and may vary over the contrasts amongst the means of the term. So the LSDs should be used with caution. (If you are interested in a specific comparison, you should set up a 2-level factor to fit this explicitly in the analysis.)

   The TERMS parameter specifies a model formula to define the fixed terms whose predicted means are to be compared. The means are usually taken from the most recent analysis performed by REML, but you can set the SAVE option to a save structure from another REML if you want to examine means from an earlier analysis. As in VCOMPONENTS, the FACTORIAL option sets a limit on the number of factors in each term (default 3).

   Printed output is controlled by the PRINT option, with settings:

    means
prints the means;

    sed
prints standard errors for differences between the means;

    lsd
prints least significant differences for the means;

    df
prints the degrees of freedom used to calculate the t critical value required for the LSD, together with the denominator degrees of freedom in the F test for the term if these are not the same.

The significance level to use in the calculation of the least significant differences can be changed from the default of 5% using the LSDLEVEL option.

   The MEANS parameter can save the means. If the TERMS parameter specifies a single term, MEANS must be undeclared or set to a table. If TERMS specifies several terms, you must supply a pointer which will then be set up to contain as many tables as there are terms. Similarly the SED parameter can save the standard errors of differences, the LSD parameter can save the approximate least significant differences, the DF parameter can save the degrees of freedom used to calculate the t-statistics, and the DDF parameter can save the denominatgor degrees of freedom in the F tests.

 

Options: PRINT, FACTORIAL, LSDLEVEL, SAVE.

Parameter: TERMS, MEANS, SED, LSD, DF, DDF.