DCdensity function

McCrary Sorting Test

DCdensity implements the McCrary (2008) sorting test.

DCdensity(runvar, cutpoint, bin = NULL, bw = NULL, verbose = FALSE,
  plot = TRUE, ext.out = FALSE, htest = FALSE)

Arguments

• runvar: numerical vector of the running variable
• cutpoint: the cutpoint (defaults to 0)
• bin: the binwidth (defaults to 2*sd(runvar)*length(runvar)^(-.5))
• bw: the bandwidth to use (by default uses bandwidth selection calculation from McCrary (2008))
• verbose: logical flag specifying whether to print diagnostic information to the terminal. (defaults to FALSE)
• plot: logical flag indicating whether to plot the histogram and density estimations (defaults to TRUE). The user may wrap this function in additional graphical options to modify the plot.
• ext.out: logical flag indicating whether to return extended output. When FALSE (the default) DCdensity will return only the p-value of the test. When TRUE, DCdensity will return the additional information documented below.
• htest: logical flag indicating whether to return an "htest" object compatible with base R's hypothesis test output.

Returns

If ext.out is FALSE, only the p value will be returned. Additional output is enabled when ext.out is TRUE. In this case, a list will be returned with the following elements: - theta: the estimated log difference in heights at the cutpoint

• se: the standard error of theta

• z: the z statistic of the test

• p: the p-value of the test. A p-value below the significance threshhold indicates that the user can reject the null hypothesis of no sorting.

• binsize: the calculated size of bins for the test

• bw: the calculated bandwidth for the test

• cutpoint: the cutpoint used

• data: a dataframe for the binning of the histogram. Columns are cellmp (the midpoints of each cell) and cellval (the normalized height of each cell)

Examples

#No discontinuity
x<-runif(1000,-1,1)
DCdensity(x,0)

#Discontinuity
x<-runif(1000,-1,1)
x<-x+2*(runif(1000,-1,1)>0&x<0)
DCdensity(x,0)

Author(s)

Drew Dimmery <drewd@nyu.edu >

References

McCrary, Justin. (2008) "Manipulation of the running variable in the regression discontinuity design: A density test," Journal of Econometrics. 142(2): 698-714. http://dx.doi.org/10.1016/j.jeconom.2007.05.005