[R] rpart - classification and regression trees (CART)

[Terry Therneau]

When two variables have exactly the same figure of merit, they will be
listed in the output in the same order in which they appeared in your
model statement.  
   Terry Therneau

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I had a question regarding the rpart command in R.  I used seven
continuous
predictor variables in the model and the variable called "TB122" was
chosen
for the first split.  But in looking at the output, there are 4
variables
that improve the predicted membership equally (TB122, TB139, TB144, and
TB118) - output pasted below.

Node number 1: 268 observations,    complexity param=0.6
  predicted class=0  expected loss=0.3
    class counts:   197    71
   probabilities: 0.735 0.265 
  left son=2 (188 obs) right son=3 (80 obs)
  Primary splits:
      TB122 < 80  to the left,  improve=50, (0 missing)
      TB139 < 90  to the left,  improve=50, (0 missing)
      TB144 < 90  to the left,  improve=50, (0 missing)
      TB118 < 90  to the left,  improve=50, (0 missing)
      TB129 < 100 to the left,  improve=40, (0 missing)

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