Regression w/o intercept in Spotfire
How to fit a regression model - without intercept in Spotfire? or for the same problem, if I write a function in R then how to import/call that function in Spotfire? Is it required to have TERR console installed in my system? I am using TIBCO Spotfire Analyst 7.6.1.
(1) Answer
In the text field named "Formula expression (column names quoted with backticks)" at the bottom of Spotfire's "Tools > Regression Modeling" dialog, you can specify a zero intercept by typing -1 at the end of the formula.
For example, if you have used the dialog's point-and-click options to define the following formula expression:
`Fuel` ~ `Weight`
you can edit it to read as follows, to specify a zero intercept in the regression model:
`Fuel` ~ `Weight` - 1
With this change, the resulting model's "Coefficients" component will list a coefficient for the Weight column, but it will not list an intercept, because the formula has defined the model's y-intercept to be zero.
For more information, you can open a TERR Console session (by selecting "Tools > TERR Tools > Launch TERR Console" from the Spotfire desktop client's main menu), then issue the following commands to open relevant TERR help files in a web browser:
?lm
?formula.object
The following item among the examples in the 'formula.object' help file illustrates how this would be done in a TERR Console session:
# no intercept
lm(Fuel ~ Weight - 1, data=fuel.frame)
