pbc<-read.table('A:/pbcWH.txt',header=T)
pbc2<-pbc[pbc$status==2,]  # use only uncensored subjects
#pbc3<-na.omit(pbc2)  #omit missing values
attach(pbc2); dim(pbc2) # 161  20
ageyr<-age/365.25  # age in years

y<-log(time)

hist(y) # not too bad w.r.t. normality

plot(ageyr,y)
lines(lowess(ageyr,y))  #linear

fit1<-lm(y~ageyr+edema)  # reduced model
summary(fit1)

names(fit1)

anova(fit1)
           Df  Sum Sq Mean Sq F value    Pr(>F)    
ageyr       1   2.464   2.464  2.7424    0.0997 .  
edema       1  31.610  31.610 35.1856 1.829e-08 ***
Residuals 158 141.943   0.898  

edema1<-ifelse(edema==0.5,1,0)
edema2<-ifelse(edema==1,1,0)
fit2<-lm(y~ageyr+edema1+edema2)
anova(fit2)
           Df  Sum Sq Mean Sq F value    Pr(>F)    
ageyr       1   2.464   2.464  2.7285   0.10057    
edema1      1   2.664   2.664  2.9498   0.08786 .  
edema2      1  29.125  29.125 32.2554 6.382e-08 ***
Residuals 157 141.764   0.903                    

# F test
> (29.125+2.664-31.610)/0.903
[1] 0.1982281
# not significant. continuous edema term is sufficient.