 Accordingly, the treatment coefficients in those regressions are not robust to heterogeneous effects across groups and over time , and may also be contaminated by the effect of other treatments.
<coherence>  Accordingly, the treatment coefficients in those regressions are not robust to heterogeneous effects across groups and over time , and may also be contaminated by the effect of other treatments.
 Accordingly, the treatment coefficients in those regressions are not robust to heterogeneous effects across groups and over time , and may be contaminated by the effect of other treatments.