I'm learning R and trying to understand how
lm() handles factor variables & how to make sense of the ANOVA table. I'm fairly new to statistics, so please be gentle with me.
Here's some movie data from Rotten Tomatoes. I'm trying to model the score of each movie based on the mean scores for all of the movies in 4 groups: those rated G, PG, PG-13, and R.
download.file("http://www.rossmanchance.com/iscam2/data/movies03RT.txt", destfile = "./movies.txt") movies <- read.table("./movies.txt", sep = "\t", header = T, quote = "") lm1 <- lm(movies$score ~ as.factor(movies$rating)) anova(lm1)
and the ANOVA output:
## Analysis of Variance Table ## ## Response: movies$score ## Df Sum Sq Mean Sq F value Pr(>F) ## as.factor(movies$rating) 3 570 190 0.92 0.43 ## Residuals 136 28149 207
I understand how to get all the numbers in this table, EXCEPT
Sum Sq and
Mean Sq for
as.factor(movies$rating). Can someone please explain how that
Sum Sq is calculated from my data? I know that
Mean Sqis just
Sum Sq divided by