[R] defining lower part of distribution with covariate

[Troels Ring]

Dear friends, forgive me a simple question, possibly related to quantreg 
but I failed to get it done and hope for basic instruction.

I have two sets of observed Glasgow coma scores at admission to ICU after 
operation, and accompanying time of anesthesia (in hours).
Thio is cheap and perhaps old fashioned, and ultiva expensive and rapidly 
terminated. The problem is to estimate the probability of GCS 12 or lower 
on the two treatments after taking time of anesthesia into account (antime) 
which is longer for thio. How would I do that in the best way ?

Best wishes
Troels Ring, MD
Aalborg, Denmark


thio
       GCS antime
  [1,]  14    4.5
  [2,]  15    7.5
  [3,]  11    7.5
  [4,]  15    4.5
  [5,]  14    4.5
  [6,]  15    3.5
  [7,]  15    5.5
  [8,]  14    5.5
  [9,]  15    3.5
[10,]  14    8.5
[11,]  13    4.5
[12,]  12    5.5
[13,]  15    3.5
[14,]  13    6.5
[15,]   9    8.5
[16,]  15    6.5
 > ultiva
       GCS antime
  [1,]  15    4.5
  [2,]  15    4.5
  [3,]  15    2.5
  [4,]  15    3.5
  [5,]  15    3.5
  [6,]  12    5.5
  [7,]  15    4.5
  [8,]  15    3.5
  [9,]  15    8.5
[10,]  13    4.5
[11,]  14    3.5
[12,]  14    4.5
[13,]  15    4.5
[14,]  14    2.5
[15,]  15    4.5
[16,]  15    3.5
[17,]  15    3.5
[18,]  14    4.5
[19,]  14    4.5
[20,]  15    4.5