Transformation Dialog
Transformation in Linear Regression
Forward Library Help

Model Page:

Data Set:

The data to be used in the Forward Search. By default only the data frames in the current working directory are displayed. However, any data frame on the search path (for instance fuel.frame) may be selected by typing its name into the Data Set combo box.

Use Example Data

Selecting this option causes the Data Set combo box to list the data frames containing the example data provided with the Forward Library. Additionally, when this option is selected the formula will be filled in automatically.

Omit Rows with Missing Values

If this option is selected, rows in the data frame that contain missing values (NA's) will be removed. Otherwise an error will be generated if missing values are present.


Specifies the dependent variable in the linear regression model.


Specifies the independent (explanatory) variable(s) in the linear regression model. Use control-clicks to select multiple variables. For more compilcated models select the data (in the Data Set combo box) and press the Create Formula button.

Remove Intercept

Selecting this option causes the intercept term to be removed from the model.

LMS Subsets:

The initial subset for the Forward Search in Linear Regression is found by fitting the regression model with the Splus function lmsreg. This option allows the user to control how many subsets are used in the Least Median of Squares regression. The choices are standard (which uses 3000 subsets) and all. Additionally, a specific number of subsets may be specified by typing a number in to the LMS Subsets combo box.

Show Progress in Report

Prints a message in the report window for every ten iterations completed during the forward search.

Values of Lambda Group

Select the values of the transformation parameter lambda to test in the forward search. To select values that do not have check boxes edit the "Values of lambda:" string at the bottom of the group. Any S expression that evaluates to a a numeric vector is acceptable. For example, to test the values {-2.0, 0, 2.0} enter (without the quotes) "c(-2.0, 0, 2.0)".

Results Page:

Short Output

This will display a brief summary of the Forward Search.

Long Output

This option provides a more detailed summary of the Forward Search. The last Steps (see below) of the diagnostic statistics monitored during the search are displayed.


Controls how many steps are shown in the summary when Long Output is selected. The default behavior ("auto") is to show either the last 5 steps or the last 10% of the search, which ever is greater. Selecting "all" will display the statistics for the entire search and selecting "user" will allow you to enter the desired number of steps in the Number of Steps field.

Number of Steps:

If the "user" option is selected in Steps then the desired number of Steps should be entered here.

MLE of Lambda in Final Step

Include the maximum likelihood estimate of lambda in the final step?

Save As:

The Forward Search is saved as an S object with (S version 3) class "fwdlm" in the current working directory. If you do not wish to save the results simply leave this field blank.

Plots Page:

Score Test Statistics

Fan Plot: plots the score test statistics for each value of lambda through the forward search.

ylim: FanPlot:

The range of the fan plot. This should be a numeric vector of length 2 containing the lower and upper bounds for the plot. For example, c(-5, 5) would set the range to show values between -5 and 5.

Confidence Level:

The value used to draw the confidence interval in the fan plot.


Plots the likelihood for each subset during the forward search.