TRY directive

Displays results of single-term changes to a linear, generalized linear or generalized additive model.


Options

PRINT = strings
What to print (model, deviance, summary, estimates, correlations, fittedvalues, accumulated, monitoring, changes); default chan

FACTORIAL = scalar
Limit for expansion of model terms; default * i.e. that in previous TERMS statement

POOL = string
Whether to pool ss in accumulated summary between all terms fitted in a linear model (yes, no); default no

DENOMINATOR = string
Whether to base ratios in accumulated summary on rms from model with smallest residual ss or smallest residual ms (ss, ms); default ss

NOMESSAGE = strings
Which warning messages to suppress (dispersion, leverage, residual, aliasing, marginality, vertical, df, inflation); default *

FPROBABILITY = string
Printing of probabilities for variance and deviance ratios (yes, no); default no

TPROBABILITY = string
Printing of probabilities for t-statistics (yes, no); default no

SELECTION = strings
Statistics to be displayed in the summary of analysis produced by PRINT=summary, seobservations is relevant only for a Normally distributed response, and %cv only for a gamma-distributed response (%variance, %ss, adjustedr2, r2, seobservations, dispersion, %cv, %meandeviance, %deviance, aic, sic); default %var, seob if DIST=normal, %cv if DIST=gamma, and disp for other distributions


Parameter

    formula
List of explanatory variates and factors, or model formula


Description

TRY investigates modifications to the current regression model, which may be linear, generalized linear or generalized additive. Terms in the specified formula are dropped from the current model if they are already there, or are added to it if they are not. It is best to give a TERMS statement before using TRY to define a common set of units for the models to be investigated. If no model is fitted after the TERMS statement, the current model is taken to be the null model.

   The default setting, changes, of the PRINT option summarises the effects of the changes after they have all been tried. Other settings request further details of the changed models. These are printed after each change. GenStat then restores the original model before trying the next change.

   The options of TRY are otherwise the same as those of the FIT directive, except that there is no CONSTANT option. The accumulated setting of the PRINT option will show only one change at a time. Accumulated summaries produced by later statements will not have any entries for a TRY statement.

 

Options: PRINT, FACTORIAL, POOL, DENOMINATOR, NOMESSAGE, FPROBABILITY, TPROBABILITY, SELECTION.

Parameter: unnamed.


Action with RESTRICT

If a TERMS statement was given before fitting the model, any restrictions on the variates or factors in the model will have been implemented then. So any new restrictions on vectors involved in the model specified by TRY will be ignored. If no TERMS statement has been given and TRY involves new terms not already in the model, restrictions on the variates or factors in these terms will be taken into account and may cause the units involved in the regression to be redefined.