Teffects stata 12
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However, for ATET the adjustment can be positive or negative, so the standard errors reported by psmatch2 may be too large or to small. Interestingly, the adjustment for ATE is always negative, leading to smaller standard errors: matching based on estimated propensity scores turns out to be more efficient than matching based on true propensity scores.
#Teffects stata 12 how to#
Harvard University and National Bureau of Economic Research) established how to take into account that propensity scores are estimated, and teffects psmatch relies on their work. Matching on the estimated propensity score. The output of psmatch2 includes the following caveat:Ī recent paper by Abadie and Imbens (2012. Treatment-effects estimation Number of obs = 1000 The teffects command reports the same ATET if asked: But note that psmatch2 is reporting a somewhat different ATT in this model. The ATE from this model is very similar to the ATT/ATET from the previous model.
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does not take into account that the propensity score is estimated. Teffects psmatch (y) (t x1 x2) Treatment-effects estimation Number of obs = 1000 Running teffects with the default options gives the following:
#Teffects stata 12 plus#
But note that teffects reports a very different standard error (we'll discuss why that is shortly), plus a Z-statistic, p-value, and 95% confidence interval rather than just a T-statistic. The average treatment effect on the treated is identical, other than being rounded at a different place. Teffects psmatch (y) (t x1 x2, probit), atet Treatment-effects estimation Number of obs = 1000Įstimator : propensity-score matching Matches: requested = 1 So to run the same model using teffects type: The teffects command uses a logit model by default, but will use probit if the probit option is applied to the treatment equation. Second, psmatch2 by default uses a probit model for the probability of treatment. The teffects command by default reports the average treatment effect (ATE) but will calculate the average treatment effect on the treated (which it refers to as ATET) if given the atet option. First, psmatch2 by default reports the average treatment effect on the treated (which it refers to as ATT). However, the default behavior of teffects is not the same as psmatch2 so we'll need to use some options to get the same results. Teffects psmatch ( outcome) ( treatment covariates) The basic syntax of the teffects command when used for propensity score matching is: You can carry out the same estimation with teffects. Variable Sample | Treated Controls Difference S.E. The psmatch2 command will give you a much better estimate of the treatment effect: (Regressing y on t, x1, and x2 will give you a pretty good picture of the situation.) Thus simply comparing the mean value of y for the treated and untreated groups badly overestimates the effect of treatment: However, the probability of treatment is positively correlated with x1 and x2, and both x1 and x2 are positively correlated with y. This is constructed data, and the effect of the treatment is in fact a one unit increase in y. It consists of four variables: a treatment indicator t, covariates x1 and x2, and an outcome y. Run the following command in Stata to load an example data set: We thus strongly recommend switching from psmatch2 to teffects psmatch, and this article will help you make the transition. This often turns out to make a significant difference, and sometimes in surprising ways. The teffects psmatch command has one very important advantage over psmatch2: it takes into account the fact that propensity scores are estimated rather than known when calculating standard errors. However, Stata 13 introduced a new teffects command for estimating treatments effects in a variety of ways, including propensity score matching. Note: readers interested in this article should also be aware of King and Nielson's 2019 paper Why Propensity Scores Should Not Be Used for Matching.įor many years, the standard tool for propensity score matching in Stata has been the psmatch2 command, written by Edwin Leuven and Barbara Sianesi.