[R] Help for survival curves for the survfit object‏

[于慧琳]

Hi guy,I have some problems when plotting survival curves for the survfit object.My survfit model is as follows:fit6<-survfit(Surv(Survival_time_year_,event)~Race_1_Desc,data=data6)Race_1_Desc is a indicator variable which has 0 and 1 values.However, in my dataset, all of the Race_1_Desc are of value 0, which means I have only 1 group.When I plot my survival curve use the following command,plot(fit6,col=c("blue","red"),xlab="Survival Time",ylab="Survival Probability",main="Survival Plot for Leaf 6")  It is correct that I only has one curve for Race_1_Desc coded as 0, which is the blue full line. But there are also two dashed line, one is red and one is blue.I just want to know what are the two dashed lines mean and why the show up in the plot.
 		 	   		  
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