ADD directive

Adds extra terms to a linear, generalized linear, generalized additive or nonlinear model.


Options

PRINT = strings
What to print (model, deviance, summary, estimates, correlations, fittedvalues, accumulated, monitoring); default mode, summ, esti

NONLINEAR = string
How to treat nonlinear parameters between groups (common, separate, unchanged); default unch

CONSTANT = string
How to treat the constant (estimate, omit, unchanged, ignore); default unch

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, 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

ADD adds terms to the current regression model, which may be linear, generalized linear, generalized additive, standard curve or nonlinear. It is best to give a TERMS statement before investigating sequences of models using ADD, in order to define a common set of units for the models that are to be explored. If no model has been fitted since the TERMS statement, the current model is taken to be the null model.

   The model fitted by ADD will include a constant term if the previous model included one, and will not include one if the previous model did not. You can, however, change this using the CONSTANT option.

   The options of ADD are almost all the same as those of the FIT directive, and are described there. There is also an extra option NONLINEAR. This is relevant when fitting curves. For example, if we have a variate Dilution and a factor Solution, the program below will fit parallel curves for the different solutions.

MODEL Density

TERMS Dilution * Solution

FITCURVE [PRINT=model,estimates; CURVE=logistic] \

  Dilution + Solution

If we then put

ADD Dilution.Solution

the curves are still constrained to have common nonlinear parameters, but all linear parameters are estimated separately for each group. Alternatively, if we put

ADD [NONLINEAR=separate] Dilution.Solution

different nonlinear parameters will be estimated for each solution too; so only the information about variability is pooled.

 

Options: PRINT, NONLINEAR, CONSTANT, 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 restrictions on vectors involved in the model specified by ADD will be ignored. If no TERMS statement has been given and ADD introduces new terms into 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.