SO5032: Lab Materials
Table of Contents
1 Week 6 Lab
1.1 Non-linearity
1.1.1 Sketch a quadratic function
Using pen and paper and/or Excel, plot the curve \(Y=20+0.75X-0.03X^2\).
1.1.2 Age example
Age often has non-linear effects: how to handle it?
use http://teaching.sociology.ul.ie/so5032/example1 recode age = . if age < 15 drop if income >6000 scatter income age, mfcol(blue%05) mlcolor(white%00) reg income age reg income age if age<=34 reg income age if age>34 gen ageg = 5*int(age/5) reg income c.ageg##c.ageg
1.1.3 Model a non-linear relationship
Run this do-file to load data on
do http://teaching.sociology.ul.ie/so5032/birth
Fit models predicting birth rate using GNP as
- a linear effect
- a quadratic effect (GNP plus squared GNP)
- logged GNP and
- a grouped effect.
Consider the fit of the four models.
Plot the four predicted values as lines/curves on the same graph: how do they compare? Plot the residuals as well.
1.2 Predicting house prices :noexport
Data on house price and characteristics are available in this do file.
do http://teaching.sociology.ul.ie/so5032/labs/agrestiHousePrice.do
Using t-tests on individual parameters, and overall F-tests/adjusted R2, search for a good model to predict house price. Use dummy variables where appropriate (see note on dummy variables in Lab 4).
Are any of the explanatory variables "multi-collinear"? Note what happens to the model when you add a variable that is collinear with one already in the equation.