(a) Does table 1 in Schneider et al show the sample is representative or unrepresentative?

(b) What percentage of the sample had incomes below $20,000?

(c) Why isn’t there an income variable in table 2? table B1?

(d) To what extent have Schneider et al stated the model? the statistical assumptions?

(e) Are Schneider et al trying to estimate the effect of an intervention?
If so, what is that intervention?