Patricia: Thank you for your question. There are two separate issues here. Specific development outcomes, such as the number of children immunized or finishing primary school, are not difficult to measure, and we have methods of measuring the counterfactual--how many children would have been immunized without the aid or the government program. The problem here is not that it's technically difficult to measure, but that it's sometimes politically difficult to get governments and aid donors to use this information and adjust their programs accordingly. Few people want to know that their favorite aid program was not productive after all. This is also why not enough resources are channeled to measuring the impact of development programs. This is a separate issue from the one I was referring to in my post, which is that if aid is aimed at preventing a growth collapse, it's difficult to measure what the actual effect of that aid was (because we cannot measure the growth deceleration in the absence of aid). Such broad questions such as aid and growth don't lend themselves to randomized impact evaluations, which is one of the techniques used to answer the narrower question of the relationship between an aid or government program and the number of children immunized.