Berk Ozler over at Development Impact has a follow up post on GiveDirectly’s three-year impacts. The post looks at multiple papers analyzing results from the same cash transfer RCT in southwestern Kenya:
First, on the initial studies:
On October, 31, 2015, after the release of the HS (16) working paper in 2013, but before the eventual journal publication of HS (16), Haushofer, Reisinger, and Shapiro released a working paper titled “Your Gain is My Pain.” In it, they find large negative spillovers on life satisfaction (a component of the psychological wellbeing index reported in HS 16) and smaller, but statistically significant negative spillovers on assets and consumption. The negative spillover effects on life satisfaction, at -0.33 SD and larger than the average benefit on beneficiaries, imply a net decrease in life satisfaction in treated villages. Furthermore, the treatment (ITT) effects are consistent with HS (16), but the spillover effects are not. For example, the spillover effect on the psychological wellbeing index in Table III of HS (16) is approximately +0.1, while Table 1 in HRS (15) implies an average spillover effect of about -0.175 (my calculations: -0.05 * (354/100)). There appear to be similar discrepancies on the spillovers implied for assets and consumption in the HRS (15) paper and HS (16). I am not sure what to make of this, as HRS (15) is an unpublished paper – there must [be] a good explanation that I am missing. Regardless, however, these findings of negative spillovers foreshadow the three-year findings in HS (18), which I discuss next.
Then on the three-year findings:
As I discussed earlier this week, HS (18) find that if they define ITT=T-S, virtually all the effects they found at the 9-month follow-up are still there. However, if ITT is defined in the more standard manner of being across villages, i.e. ITT=T-C, then, there is only an effect on assets and nothing else.
… As you can see, things have now changed: there are spillover effects, so the condition for ITT=T-S being unbiased no longer holds. This is not a condition that you establish once in an earlier follow-up and stick with: it has to hold at every follow-up. Otherwise, you need to use the unbiased estimator defined across villages, ITT=T-C.
To nitpick with the authors here, I don’t buy that [….] lower power is responsible for the finding of no significant treatment effects across villages. Sure, as in HS (16), the standard errors are somewhat larger for across-village estimates than the same within-village estimates. But, the big difference between the short- and the longer-term impacts is the gap between the respective point estimates in HS (18), while they were very stable (due to no/small spillovers) in HS (16). Compare Table 5 in HS (18) with Appendix Table 38 and you will see. The treatment effects disappeared, mainly because the differences between T and C are much smaller now, and even negative, than they were at the nine-month follow-up.
And then this:
If we’re trying to say something about treatment effects, which is what the GiveDirectly blog seems to be trying to do, we already have the estimates we want – unbiased and with decent power: ITT=T-C. HS (18) already established a proper counterfactual in C, so just use that. Doesn’t matter if there are spillovers or not: there are no treatment effects to see here, other than the sole one on assets. Spillover estimation is just playing defense here – a smoke screen for the reader who doesn’t have the time to assess the veracity of the claims about sustained effects.
Bottom line: we need more research on UCTs, which GiveDirectly is already doing with a (hopefully) better-implemented really long-term study.