METHODOLOGY 33
organizations in the provision of extension and other agriculture-related ser- vices in rural areas. These organizations operate mostly through farmer groups and associations. For example, in their study on Uganda, Jagger and Pender (2003) found that the presence of an organization dealing with agriculture and environment-related issues such as household membership in such an organization is significantly associated with adoption of several agricultural and sustainable land management technologies. Thus by including household membership in other organizations as an explanatory variable in our model specification and estimation, we expect to reduce the overattribution prob- lem, although we realize that the variable does not exhaustively capture variation in individual information solicitation. Jagger and Pender (2003) show that household involvement or membership in such organizations is signifi- cantly influenced by several of the factors discussed earlier.
Other Estimation Issues and Interpretation of Empirical Results Unless otherwise stated, all monetary values were converted to 2000 con- stant values using the consumer price index as the deflator. This helped us to exclude the influence of inflation and other temporal monetary and fiscal trends. Based on the stratified sampling approach used in the survey data collection, all the sample statistics and estimates associated with the 2SWR estimator were corrected for stratification, clustering, and weighting of sam- ple. We are unaware of how to fully correct for all of these features with the matching methods. With the PSM method, we tried to correct for stratifica- tion by first performing the matching within each stratum and then estimated the ATT for each stratum using bootstrapping to estimate the standard errors. Then we used a weighted average procedure to obtain the ATT for the whole sample by using the average sampling weight for each stratum as the weight. The implication of this on the resulting estimates is that they will approach the true values to the extent that the within-group and across-group varia- tions in the sampling weights are similar within a particular stratum.10 To assess the sensitivity of the results in correcting for stratification, clustering, and weighting of sample, we estimated the 2SWR without and with perform- ing the correction.
Typically, correction for stratification, clustering, and weighting of sam- ple requires correct calculation of the standard errors of the estimates for reliable statistical inference. All the analyses in this study were carried out
10 For further details on these issues with the matching methods, see Leuven and Sianesi (2003) on how to match within strata and obtain the average effects for the whole population and Abadie et al. (2004) on how to handle probability sampling weights in nearest-neighbor match- ing estimators.
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