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I am trying to run a parametric RD regression using the rddtools R package. However, the package documentation is not very clear to me.

First: the function to define an RD object is: rdd_data(y, x, covar, cutpoint, z, labels, data)

where covar, in the help file, means only "Exogeneous variables" . But what type? A data frame? A list?

Second: The function rdd_reg_lm again demands informing covariates in this way:

rdd_reg_lm(rdd_object, covariates = NULL, order = 1, bw = NULL,
  slope = c("separate", "same"), covar.opt = list(strategy = c("include",
  "residual"), slope = c("same", "separate"), bw = NULL),
  covar.strat = c("include", "residual"), weights)

Where, according to the help file, the covariates argument means simply "Formula to include covariates". Again, it is not clear to me what is exactly the correct way of applying these covariates.

Moreover, is it possible to include multiple covariates in this function rdd_data() and rdd_reg_lm()?

I appreciate some help here. I have already read the help and vignette files again and again, searched in many blogs and still nothing.

I have already checked this topic below

How to include a linear trend in a regression discontinuity design using rddtools

which showed me the following example:

rd.medic <- rdd_data(y = er ,x = ageyrs, covar = ageyrs, cutpoint=65, data = medicare)

rd.reg <- rdd_reg_lm(rdd_object=rd.medic, covariates = 'ageyrs', slope =
("same"), covar.opt = list("include"))

Even so, the syntax is still not clear to me, as I am trying to add multiple covariates without success

Thanks!

José Eduardo Sousa
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1 Answers1

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You can create a data frame with your covariates and then include it in rdd_data.

covariates<-data.frame(z1=ageyrs, z2=ageyrs2)

rd.medic <- rdd_data(y = er ,x = ageyrs, covar = covariates, cutpoint=65, data = medicare)

rd.reg <- rdd_reg_lm(rdd_object=rd.medic, covariates =TRUE, slope =("same"))
randomperson
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