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## Trying to figure out what R is doing with anova's | |
# The difference of aov() and lm() simply changes how summary() acts | |
# summary(aov()) is the same as anova(lm(), which are both TYPE 1! | |
# for type = III SS you need to use Anova in the library(car) package | |
# https://rcompanion.org/rcompanion/d_04.html | |
# Different SS primer | |
# https://stats.stackexchange.com/questions/20452/how-to-interpret-type-i-type-ii-and-type-iii-anova-and-manova/20455#20455 | |
# http://www.utstat.utoronto.ca/reid/sta442f/2009/typeSS.pdf | |
# my attempt | |
df <- mtcars | |
df$cyl <- as.factor(df$cyl) | |
# first summary responding to the class of objects | |
mod_lm <- lm(mpg ~ disp + hp + cyl, data = df) | |
mod_lm_sw <- lm(mpg ~ hp + disp + cyl, data = df) | |
mod_aov <- aov(mpg ~ disp + hp + cyl, data = df) | |
mod_aov_sw <- aov(mpg ~ hp + disp + cyl, data = df) | |
summary(mod_lm) | |
summary(mod_lm_sw) # NOTHING CHANGES | |
summary(mod_aov) | |
summary(mod_aov_sw) # TYPE 1!!!! | |
# summary has different behaviour dependent on class of mod | |
# anova reacts the same... is it class III? | |
library(car) | |
anova(mod_lm) | |
anova(mod_lm_sw) # TYPE 1!!! | |
anova(mod_aov) | |
anova(mod_aov_sw) # TYPE 1?? | |
# these 4 act the same way as summary(aov()) | |
Anova(mod_lm, type = "III") | |
Anova(mod_lm_sw, type = "III") | |
Anova(mod_aov, type = "III") | |
Anova(mod_aov_sw, type = "III") | |
# acts the same regardless of mod type, this is type III SS | |
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