[R] Survival analysis

[cpoiw@rt m@iii@g oii chemo@org@uk]

On 2020-04-17 20:06, Medic wrote:
> I can't understand how to do a survival analysis (?Surv ()) when some
> event occurred before the start of observation (left censored). If I
> understand correctly, there are two methods. I chose a method with: 1)
> time from the start of treatment to the event and 2) the indicator of
> the event. I did (in my data) the event indicator so:
> 1 - event, 2 - event before the start of observation, 0 - no event

I have no experience of left censoring beyond the text book.  Is your 
left censored data the SAME event or a different event?

> ---
> library(survival)
> left_censor_data <- read.table("left.csv", header = TRUE, sep = ";")
> #sep = ";" it's right!
> dput(left_censor_data, file="left_censor_data") #file attached
> left_censor_data
>    'data.frame':   11 obs. of  2 variables:
>    $ timee : int  5 151 33 37 75 14 7 9 1 45 ...
>    $ eventt: int  2 0 0 0 0 0 0 2 0 1 ...
>    # 1—event, 2 – event before the start of observation , 0 – no event
> 

So if I read this data correctly the first observation is left censored. 
  What does the time "5" refer to?  Is that 5 days BEFORE observation the 
event happened?  Or 5 days after another event happened?  My text book 
understanding of left censored data was that your censored points would 
have time 0.

> sur <- Surv(time = left_censor_data$timee,  event =
> left_censor_data$eventt, type = "left")
>   Warning message:
>   In Surv(time = left_censor_data$timee, event = 
> left_censor_data$eventt,  :
>   Invalid status value, converted to NA
> 
> #Why such a message?
> #Then everything turns out wrong


Is the censoring type you want LEFT TRUNCATION rather than LEFT.  If 
they are also right censored I think R Surv calls these Counting.

See: https://folk.ntnu.no/bo/TMA4275/Download/R.tutorialDiez.pdf

Any help?