Contents
What are factor interactions?
An interaction between factors is when the effect of one factor is dependent on the conditions in the other factor. If there is no interaction, then the two factors are acting independently.
What is a factor in a linear model?
A linear factor model relates the return on an asset (be it a stock, bond, mutual fund or something else) to the values of a limited number of factors, with the relationship described by a linear equation.
What are factor variables?
Factor variables are categorical variables that can be either numeric or string variables. Factor variables are also very useful in many different types of graphics. Furthermore, storing string variables as factor variables is a more efficient use of memory. To create a factor variable we use the factor function.
How are levels of factors after a GLM validated?
As the number of prey is limited (25 available) in each trial, I had a column “Sample” representing the number of available prey (so, 25 in each trial), and another called “Count” which was the number of success (how many prey were eaten). I based my analysis on the example from the R book on proportion data (page 578).
When to use Coeff and interpretation of interaction terms?
Now comes the question of interpreting coeff when you have interaction terms. Imagine a simple linear model: y ~ x1 + x2. The coeff of x1 or x2 indicates the increase in y with a unit increase in x1 or x2 respectively. However, the moment you add an interaction term, interpretation is not so easy.
Which is the interpretation of an interaction term?
However, the moment you add an interaction term, interpretation is not so easy. If you increase x1 by 1 unit in a model: y = b0 + b1 x1 + b2 x2 + b3 x1:x2, the increase in y is : b1 + b3*x2. As you see the increase is not linear, it depends on the level of x2.
Is the tukeyhsd function used in a GLM?
If I had a linear model, I would use the TukeyHSD function, but as I am using a GLM I can’t. I have been looking through the package MASS and trying to set up a contrast matrix but for some reason it doesn’t work. Any suggestions or references? Here’s the summary I get from my model, if that helps making it clearer…