Message-ID: <46954B32-E577-4167-A795-0F0F0B4ADF2E@me.com>
Date: 2010-08-03T13:34:02Z
From: Sam
Subject: factor / intiger
Dear List
I have a excel spread sheet with 5 columns that contain categorical data. I have recoded them to numbers
A B C
0 0 0
1 1 1
2 2 2
3 3
4
5
etc
When i read it into R and do str(dataframe) i get -
$ A : int 1 1 1 1 1 1 1 1 1 1 ...
$ B : int 1 1 1 1 1 1 1 1 1 1 ...
$ C : int 0 0 0 0 0 0 0 0 0 0 ...
$ D : int 0 0 0 0 0 0 0 0 0 0 ...
$ E : int 0 0 0 0 0 0 0 0 0 0 ...
I then realised they should probably be factors instead of integers so used as.factor to convert them -
A <- as.factor(A)
Now when i run the GLMM the AIC values are different from when they were integers, i have 2 questions
1. Should i not have converted the categories to numbers in the excel spreadsheet before import.
2. Why are the AIC values different when i use as.factor as opposed to keeping them as integers, and which approach is recommended?
Thanks
Sam