As it usually happens in the social "sciences," it's very naive to believe that in any of these cases we have anything like solid evidence about the total effect of the programs in question. Even ignoring the intractable problems with disentangling all the countless non-obvious confounding variables, there is still the problem of unintended consequences -- which may be unaccounted for even if the study seemingly asks all the relevant questions, and which may manifest themselves only in the longer run.

Take for example this nurse-family partnership program. Even if the study has correctly proven that these positive outcomes have occurred in the families covered by the intervention, and that they are in fact a consequence of the intervention -- a big if -- we still have no way of knowing its total long-run effect. For one, it may happen that it lowers the cost of having children for poor unmarried women, both by providing assistance and by lowering the stigma and fear of such an outcome, so that in the new long-term equilibrium, more children are born to such women, especially the least responsible, resourceful, and competent ones, eventually increasing the total measure of child poverty, neglect, abuse, etc. Of course, this may or may not be the case, but there's no way to know it based on these studies that purport to give a definitive evaluation of the program's success.