---------------- help for grlog ----------------Graphing Logistic Regression ----------------------------

To invoke, type

. grlog

This program shows the regression line between X and Y in Logistic Regression.

The first dialogue box asks you how you would like to the view the predicted value of Y in the relationship between X and Y. You can choose to view the predicted value of Y as

- the probability Y=1 This is useful for showing the S shaped curve of the relationship between X and P(Y=1). Students can see that the Y axis is easy to interpret but the shape of the relationship is not linear. - The Logit of Y (Log Odds Y=1). This is useful for showing the "logit" model, where the relationship between X and Y is linear; however, interpreting the meaning of Y is very tricky.

Also, you can choose to "Show Point at (X,Yhat)". This will display a point which is the predicted value for Y when X is 0. You will then be able to increase/decrease X to show how the predicted value of Y changes as X changes.

You can then choose "continue".

The next dialogue box allows you to adjust a-.1 and a+.1 : adding and subtracting .1 from the intercept. b-.1 and b+.1 : adding and subtracting .1 from the slope. X-1 and X+1 (if you choose "show point at predicted value of X") This allows you to add and subtract 1 from X, and see how it impacts the predicted value of Y.

You can also show 2 "movies" Show Movie Varying a : Varies a from -1 to +1, showing how varying a changes the logistic regression curve.

Show Movie Varying b : Varies b from -1 to +1, showing how varying b changes the logistic regression curve.

The "Done" button quits the program. The "Reset" button resets a, b and X to their default values, i.e., a=0, b=1, and X=0. The "Help" button brings up this help screen. Author ------

Statistical Consulting Group Institute for Digital Research and Education, UCLA idrestat@ucla.edu