Session 2: Issues in linear regression
June 5 2008
Materials
- attachment:lexdecRT.R
- attachment:BaayenETAL06.pdf
Reading
G&H07 |
Chapter 4 (pp. 53-74) |
Linear regression: before and after fitting the model |
Baa08 |
Sections 6.2.2-6.2.4 (pp. 198-212) |
Collinearity, Model criticism, and Validation |
|
Section 6.4 (pp. 234-239) |
Regression with breakpoints |
Notes on the readings
Additional terminology
Feel free to add terms you want clarified in class:
Questions
- Q: Determining the significance of a coefficient: one-tailed or two-tailed t test?
- A: It's a two-tailed test because we cannot a-priori assume which direction the coefficient will go. I guess if one had a really strong theoretical reason
to assume one direction, you could do a one-tailed test (which is less conservative).
Q: What is really happening behind the scenes when we call the data() command?
A: Even after reading ?data, it's not totally clear what's happening. It turns out that most packages distributed with R use a database to store their data (this consists of three files (foo.rdb, foo.rds, foo.rdx)). The internal mechanism used to deal with a database like this is the function lazyLoad(). Calling lazyLoad() on a database has the effect of putting all of the objects in the database into your workspace, but the objects aren't actually filled with all of their values until you use them. This means that you can load all of the datasets from a large library like languageR without using up all of your memory. The underlying action take by a call to data() is something like
lazyLoad(file.path(system.file(package="languageR"), "data", "Rdata"))
Suggested topics
If you have any material that you would like to cover that isn't included in the list below, please make note of it here.
Assignments
Upload your solutions to this page by 10pm.
G&H07 |
Section 4.9 (p.76) |
Exercise 4 |
Baa08 |
Section 6.7 (p. 260) |
Exercise 1, 8 |
In addition to the book problems, we will distribute a data set from the ongoing ngrams project.