Dear all,

I am currently trying to use a Regression Discontinuity specification to try to estimate the effect of a policy.
In short and in a simplified way, my data contains the variable y which is the outcome, and the variable cutoff which takes the value 0 at the cutoff, and symetrically goes up and down to the right and left of the cutoff.

However, when I run the very simple code:

Code:
 rdrobust y cutoff
I get the following results:

Code:
. rdrobust y cutoff
Mass points detected in the running variable.

Sharp RD estimates using local polynomial regression.

      Cutoff c = 0 | Left of c  Right of c            Number of obs =          0
-------------------+----------------------            BW type       =      mserd
     Number of obs |    174303      147978            Kernel        = Triangular
Eff. Number of obs |     16296       20287            VCE method    =         NN
    Order est. (p) |         1           1
    Order bias (q) |         2           2
       BW est. (h) |     7.640       7.640
       BW bias (b) |    15.763      15.763
         rho (h/b) |     0.485       0.485
        Unique obs |        69          70

Outcome: y. Running variable: cutoff.
--------------------------------------------------------------------------------
            Method |   Coef.    Std. Err.    z     P>|z|    [95% Conf. Interval]
-------------------+------------------------------------------------------------
      Conventional |  .06579     .00541   12.1658  0.000     .05519      .076388
            Robust |     -          -     11.3404  0.000    .056157      .079624
--------------------------------------------------------------------------------
Estimates adjusted for mass points in the running variable.
My questions are :
- What does it mean to have mass points in the running variable? To have multiple observations for a single value of my "cutoff" variable? This is definitely my case. Is it problematic?
- I am bothered by the number of obs = 0. Does it come from this mass point problem? I still get an estimation as you can see, and I am given the number of obs to the right and left of c, so I am wondering what this 0 up there to the right means.

Thanks a lot for your help and time,
Pierre