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From | Nyasha Tirivayi <ntirivayi@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: Regression Discontinuity Design |
Date | Fri, 7 Oct 2011 16:21:00 +0200 |
Hi Austin Thank you so much for the response. I am trying to estimate the impact of a social program on intrahousehold labour supply. Hence I have labour supply data at individual level. In total I have 474 individuals from 200 treated households (residing in 4 treated communities) and 532 individuals from 200 control households (residing in 4 control communities). I had initially done propensity score matching (PSM). However baseline labour supply rates for the treated sample (68%) are lower than from the control group (57%). Once comment I have received is that the possibility of differential trends in labor market outcomes across program and non-program communities implies that any observed differences are not reliable measures of the effects of the food program. Hence journal reviewers are concerned about the possibility of unobservables and suggested a regression discontinuity approach (if possible) or within community estimates. So if I cannot use the RD approach what alternatives to PSM to deal with unobservables in cross sectional data? The study design is summarized below: Community Households Adult Individuals Community HIV rate Treated 1 50 103 22.5 2 50 120 22.6 3 50 122 22.5 4 50 129 20.3 Control 1 50 124 18.5 2 50 140 20.4 3 50 126 18.5 4 50 138 23.9 Regards N.Tirivayi Maastricht University Netherlands On Fri, Oct 7, 2011 at 1:55 PM, Austin Nichols <austinnichols@gmail.com> wrote: > Nyasha Tirivayi <ntirivayi@gmail.com> > You do not have a good RD design, partly because you do not appear to > be confident of the existence of a discontinuity in treatment, but > mainly because you do not have adequate sample size. 6 communities > are hypothesized to lie on either side of the cutoff; if assumptions > are correct, communities close to the cutoff can be treated as being > randomly assigned treatment. People in those communities can also be > treated as being randomly assigned treatment under the stronger > assumption that community is fixed and people do not change community. > But you do not have 400 observations on the assignment variable with > which to construct a local linear regression of the effect of the > assignment variable on treatment; you have 6. The problem here is that > you will really want to cluster on community, but you cannot cluster > when you have 6 clusters (and when you cluster in the first stage, you > really only have 6 obs, not 400). Even 400 obs probably would not be > enough to identify any reasonably small effect using an RD method, > which needs a very large sample size to work well. The first thing to > do in such cases, if you are not sure how much power you might have, > is to run a quick simulation. There are IV methods one might use, > perhaps based on distance to clinic, but you are not really explicit > about what your estimand is. What are you trying to estimate? What > is the outcome variable? > > On Thu, Oct 6, 2011 at 6:39 PM, Nyasha Tirivayi <ntirivayi@gmail.com> wrote: >> Hello >> >> I have questions about implementing a regression discontinuity >> approach. I have cross sectional data from 200 households on a social >> program and 200 control households. The program was targeted at two >> levels- geographically and at household level. >> >> The geographic placement of the social program in communities appears >> to have been done based on HIV prevalence rates of more than 20.5% for >> 3 "treated" communities and less than 20.5% for 3 "control >> communities". Two clinics do not follow this cutoff making it a fuzzy >> discontinuity design at community level. After geographic placement, >> households were then selected based on a means tested score. However >> we do not have access to this data. We have data from 200 randomly >> sampled households who are actually in the social program and residing >> in the treated communities and from 200 control households with >> similar household characteristics to the treated households but >> residing in the control communities. >> >> My questions are as follows: >> 1. Would it be valid to use the community level discontinuity for >> impact evaluation? What software can I use in Stata? >> 2. If so would an RD approach based on 8 communities be valid? Is the >> sample of communities too small? >> 3. If RD is no appropriate what other methods besides propensity score >> matching can I use, that can also take care of unobservables even with >> cross sectional data? >> >> Kindly advise >> >> Regards >> >> N.Tirivayi >> Maastricht University >> Netherlands > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/