Timing and Duration of Exposure in Evaluations of Social Programs
Impact evaluations aim to measure the outcomes that can be attributed to a specific policy or intervention. Although there have been excellent reviews of the different methods that an evaluator can choose in order to estimate impact, there has not...
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| Language: | English |
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World Bank, Washington, DC
2012
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| Online Access: | http://documents.worldbank.org/curated/en/2008/08/9737166/timing-duration-exposure-evaluations-social-programs http://hdl.handle.net/10986/6812 |
| Summary: | Impact evaluations aim to measure the
outcomes that can be attributed to a specific policy or
intervention. Although there have been excellent reviews of
the different methods that an evaluator can choose in order
to estimate impact, there has not been sufficient attention
given to questions related to timing: How long after a
program has begun should one wait before evaluating it? How
long should treatment groups be exposed to a program before
they can be expected to benefit from it? Are there
important time patterns in a program's impact? Many
impact evaluations assume that interventions occur at
specified launch dates and produce equal and constant
changes in conditions among eligible beneficiary groups; but
there are many reasons why this generally is not the case.
This paper examines the evaluation issues related to timing
and discusses the sources of variation in the duration of
exposure within programs and their implications for impact
estimates. It reviews the evidence from careful evaluations
of programs (with a focus on developing countries) on the
ways that duration affects impacts. |
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