
Hi, everyone.
I have some questions about quantile regression in R.
I am running an additive quantile regression first for a complete matrix and then with some selected rows.

I am doing the following:

datos <-read.table("Regresion multiple.txt",header=T)

Fit<-rqss(datos$campings ~datos$Cobarbogrupo+datos$CobSDgrupo+datos$Areadecultivosgrupo, tau=0.9)

summary.rq(Fit)

#The output is:

Coefficients:
                                          Value               Std. Error             t value             Pr(>|t|)
(Intercept)                          1.46561              0.35857               4.08733           0.00004
datos$Cobarbogrupo            0.09357              0.05064               1.84784           0.06473
datos$CobSDgrupo              -0.07328             0.01671              -4.38629           0.00001
datos$Areadecultivosgrupo   0.02706              0.02202               1.22873           0.21927
Warning message:
In summary.rq(Fit) : 1 non-positive fis


#So far, so good. Now I select a group of rows I am interested in as follows:

sub<-subset(datos, Regtur==1)
write.table(sub, "Regtur1.txt")

#And run the quantile regression again:

dato<- read.table("Regtur1.txt", header=T)

Fit<-rqss(dato$campings ~ dato$Cobarbogrupo+dato$CobSDgrupo+dato$Areadecultivosgrupo, tau=0.9)

summary.rq(Fit)

#As you can see, the commands are the same. But, I get this output:

Coefficients:
                                         coefficients            lower bd            upper bd
(Intercept)                              2.67500               -2.58710             8.81632
dato$Cobarbogrupo                  1.00000              0.66909               3.01845
dato$CobSDgrupo                     0.32500              -0.56172             1.77540
dato$Areadecultivosgrupo          -0.15000            -0.43830             0.12112
Warning message:
In rq.fit.br(x, y, tau = tau, ci = TRUE, ...) : Solution may be nonunique


My questions are these:
1) Why do I get different outputs? Why I don't get the p values for each coefficient in the second output? Is there a problem with tables?
2) Are the two outputs showing the same information? Can I interpret that if zero is included in the interval of the second output, the coefficient is not different from zero?


Thanks in advance to anyone who can help me.

Federico
 		 	   		  
	[[alternative HTML version deleted]]

