Number of "bins" with rddensity, plot

[Richard Thomas Boylan]

After rddensity, plot, I cannot figure out (1) the number of bins drawn by rddensity, plot (other than manually counting the number of rectangles on the graph),
(2) and the lowest x-value and highest x-values for the bins. Any suggestions? Example of rddensity, plot below. In this example there seem to be about 50 bins, the lowest x-value is about 0.05, and the highest x-value is 1.

clear all
use https://sscc.wisc.edu/~rdimond/real_world_tables/reg3
gen x = runiform(0,1)
gen y = 0.9*x + 0.1*nicu
rddensity y, c(0.5) plot

[Andrew Musau]

rddensity is from SSC, as you are asked to explain in FAQ Advice #12. You can ask for the estimation results to be generated.

clear all
use https://sscc.wisc.edu/~rdimond/real_world_tables/reg3
gen x = runiform(0,1)
gen y = 0.9*x + 0.1*nicu
rddensity y, c(0.5) plot genvars(z)

*(1) the number of bins drawn by rddensity
count if !missing(z_hist_height)

*(2) and the lowest x-value and highest x-values for the bins
sum z_hist_height

Res.:

. *(1) the number of bins drawn by rddensity

.
. count if !missing(z_hist_height)
  74

.
.
.
. *(2) and the lowest x-value and highest x-values for the bins

.
. sum z_hist_height

    Variable |        Obs        Mean    Std. dev.       Min        Max
-------------+---------------------------------------------------------
z_hist_hei~t |         74    1.016774    .2141698   .5255579   1.348446

[Richard Thomas Boylan]

My bad. Thank you so much for your help!

[Richard Thomas Boylan]

Under further thought, the lowest x-value and highest x-values for the bins do not seem right at all. The command you gives
.5255579 1.348446 while by looking at the picture, it should be 0.05 1.

[Richard Thomas Boylan]

Reading the help more carefully, the lower and upper bounds are

di e(c) - e(h_l)*3
di e(c) + e(h_h)*3

[Andrew Musau]

Under further thought, the lowest x-value and highest x-values for the bins do not seem right at all. The command you gives
.5255579 1.348446 while by looking at the picture, it should be 0.05 1.

Ah yes. The values represent the max and min heights of the bars "y-values". For the x-values, either jointly evaluate the minimum of z_hist_endl and the maximum of z_hist_endr or the min and max values of z_grid (preferable).

clear all
use https://sscc.wisc.edu/~rdimond/real_world_tables/reg3
gen x = runiform(0,1)
gen y = 0.9*x + 0.1*nicu
rddensity y, c(0.5) plot genvars(z)

*(1) the number of bins drawn by rddensity
count if !missing(z_hist_height)

*(2) and the lowest x-value and highest x-values for the bins
sum z_hist_endl z_hist_endr

*OR PREFERABLY
sum z_grid

Res.:

. 
. sum z_hist_endl z_hist_endr

    Variable |        Obs        Mean    Std. dev.       Min        Max
-------------+---------------------------------------------------------
 z_hist_endl |         74    .5032266    .2790622   .0390249   .9863403
 z_hist_endr |         74    .5162107    .2795202   .0514837   .9998498

. 
. 
. 
. *OR PREFERABLY

. 
. sum z_grid

    Variable |        Obs        Mean    Std. dev.       Min        Max
-------------+---------------------------------------------------------
      z_grid |         20    .5097187     .292439   .0390249   .9998498

But the bars have widths, so these represent the starting and ending values. If you want the min and max of the bars' centers:

sum z_hist_center

and with this, you get:

. sum z_hist_center

    Variable |        Obs        Mean    Std. dev.       Min        Max
-------------+---------------------------------------------------------
z_hist_cen~r |         75     .480327    .2715404   .0066127    .927862