Arthritis data: diagnostic plots

define Better

Arthritis$Better <- Arthritis$Improved > 'None'

main effects model for the binary response

arth.mod1 <- glm(Better ~ Age + Sex + Treatment , data=Arthritis, family='binomial')
Anova(arth.mod1)

## Analysis of Deviance Table (Type II tests)
## 
## Response: Better
##           LR Chisq Df Pr(>Chisq)    
## Age         6.1587  1  0.0130764 *  
## Sex         6.9829  1  0.0082293 ** 
## Treatment  12.1965  1  0.0004788 ***
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

diagnostic plots: “regression quartet”

op <- par(mfrow=c(2,2))
plot(arth.mod1)

par(op)

influence plot

influencePlot(arth.mod1, main="Arthritis data: influencePlot")

##      StudRes        Hat      CookD
## 1   1.922340 0.08968430 0.11275986
## 4   1.789163 0.08404862 0.08180053
## 15 -1.183430 0.14158260 0.04199003
## 16 -1.360860 0.09261481 0.03812094
## 39 -2.170769 0.03144317 0.06896768