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Re: st: Regression Discontinuity Design


From   Austin Nichols <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Regression Discontinuity Design
Date   Fri, 7 Oct 2011 11:10:35 -0400

Nyasha Tirivayi <ntirivayi@gmail.com> :
What do you mean, "baseline labour supply rates for the treated sample
(68%) are lower than from the control group (57%)"

fwiw, I see no evidence of a discontinuity:

clear
input T Community N HIVrate
1   1    103     22.5
1   2    120     22.6
1   3    122     22.5
1   4    129     20.3
0   5    124     18.5
0   6    140     20.4
0   7    126     18.5
0   8    138     23.9
end
sc T HIVrate [aw=N]


On Fri, Oct 7, 2011 at 10:15 AM, Nyasha Tirivayi <ntirivayi@gmail.com> wrote:
> 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. 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.
>
> CommunityHouseholdsAdult 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
>
>
>
> 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
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