Quantile regression errors and How to plot?

Hi all,

I'm running the quantile regression and trying to plot the coefficients and confidence intervals of four independent variables (yeaedu, sex, union, unimem).

The data a .dta file, but I used as_factor to convert data before running the regression.

My codes:

bri0 = read.dta("britearn.dta")
bri0.1 = as_factor(bri0,only_labelled = TRUE)

#quantile regression
model.bri.q = rq(lrehrwge ~ yeaedu + sex + union + unimem

  • seniorit + yeactexp + race + mastat
  • jbsect + region,
    data = bri0, tau = seq(0.1, 0.9, by=0.1),
    na.action = na.exclude)
    summary(model.bri.q)

My data file:
https://redirect.is/qhnxri8

My errors are:
Warning messages:

.... Solution may be nonunique

1: In summary.rq(xi, U = U, ...) : 37 non-positive fis

2: In summary.rq(xi, U = U, ...) : 9 non-positive fis

3: In summary.rq(xi, U = U, ...) : 2 non-positive fis

4: In summary.rq(xi, U = U, ...) : 9 non-positive fis

5: In summary.rq(xi, U = U, ...) : 5 non-positive fis

6: In summary.rq(xi, U = U, ...) : 7 non-positive is

So, my questions are:

  • How did I get these errors?
  • How can I plot the effects of only four variables yeaedu + sex + union + unimem on the dependent variable (most of the rest are categorical variables, I don't want to plot them)?

I'm a beginner user of R, so I hope that you can help me to resolve my problem well.

Thank you so much!

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