Hello,
I have two questions regarding a survival analysis I have been
working on. Below is the code to date.
The variables:
1) recidivism$intDaysUntilFVPO are the number of days before an
violent offence was committed - if no offence was committed than the
days between court hearing and end of data collection was recorded.
2) recidivism$intDaysUntilFNVPO are the number of days before a
nonviolent offence was committed - if no offence was committed than
the days between court hearing and end of data collection was recorded.
3) recidivism$Event_v coded TRUE or FALSE as to whether a violent
offence was committed
4) recidivism$Event_nv coded TRUE or FALSE as to whether a
non-violent offence was committed
5) recidivism$group - there were 3 groups recorded as 1, 2 or 3
I encountered two problems:
a) when I tried to run the following: >
surv_test(Surv(recidivism$intDaysUntilFVPO, recidivism$Event_v) ~
recidivism$group, data = recidivism, distribution = "exact")
I received the following error message. I am unsure whether the
problem lies with the group variable, how I have set up the time
variables or there is something missing.
Error in check(itp) :
'object' does not represent a K sample problem with censored data
(b) I ran some simple plots of the curves. While I have a fair idea
of which group is which, I wanted to add a legend identifying the
groups ? What code is required for this?
Any assistance is much appreciated,
Bob
> library(survival)
>
> survdiff(Surv(recidivism$intDaysUntilFVPO, recidivism$Event_v) ~
group, data = recidivism)
Call:
survdiff(formula = Surv(recidivism$intDaysUntilFVPO, recidivism$Event_v) ~
group, data = recidivism)
N Observed Expected (O-E)^2/E (O-E)^2/V
group=1 1136 135 154.18 2.39 7.75
group=2 446 87 61.29 10.78 14.90
group=3 65 1 7.52 5.66 5.86
Chisq= 18.9 on 2 degrees of freedom, p= 8.06e-05
> survdiff(Surv(recidivism$intDaysUntilFNVPO, recidivism$Event_nv) ~
group, data = recidivism)
Call:
survdiff(formula = Surv(recidivism$intDaysUntilFNVPO, recidivism$Event_nv) ~
group, data = recidivism)
N Observed Expected (O-E)^2/E (O-E)^2/V
group=1 1136 323 366.3 5.11 17.80
group=2 446 184 127.7 24.84 33.12
group=3 65 7 20.1 8.51 8.86
Chisq= 38.5 on 2 degrees of freedom, p= 4.3e-09
> layout(matrix(1:2, ncol = 2))
> plot(survfit(Surv(recidivism$intDaysUntilFNVPO,
recidivism$Event_v) ~ recidivism$group, data = recidivism), main =
"time to violent reoffense by group", lty = c(1,2,3), ylab =
"probability", xlab = "survival time in days")
> plot(survfit(Surv(recidivism$intDaysUntilFVPO,
recidivism$Event_nv) ~ recidivism$group, data = recidivism), main =
"time to nonviolent reoffense by group", lty = c(1,2,3), ylab =
"probability", xlab = "survival time in days")
>
> library(coin)
> surv_test(Surv(recidivism$intDaysUntilFVPO, recidivism$Event_v) ~
recidivism$group, data = recidivism, distribution = "exact")
Error in check(itp) :
'object' does not represent a K sample problem with censored data
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