2018
DOI: 10.1186/s41937-017-0004-9
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Comparative politics and the synthetic control method revisited: a note on Abadie et al. (2015)

Abstract: Recently, Abadie et al. (Am J Polit Sci 59:495–510, 2015) have expanded synthetic control methods by the so-called cross-validation technique. We find that their results are not being reproduced when alternative software packages are used or when the variables’ ordering within the dataset is changed. We show that this failure stems from the cross-validation technique relying on non-uniquely defined predictor weights. While the amount of the resulting ambiguity is negligible for the main application of Abadie e… Show more

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Cited by 42 publications
(31 citation statements)
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“…Finally, we analyze the possibilities for specification searching and provide our recommendations in a series of empirical applications. C 2020 by the Association for Public Policy Analysis and Management on behalf of the Association for Public Policy Analysis and Management variables, the choice of how to split the pre-treatment periods into training and validation periods, and even the choice of software and data-sorting criteria (see Klößner et al, 2017, for details on this last point). Therefore, our results should be seen as a lower bound on the possibilities for specification searching in SC applications.…”
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confidence: 99%
“…Finally, we analyze the possibilities for specification searching and provide our recommendations in a series of empirical applications. C 2020 by the Association for Public Policy Analysis and Management on behalf of the Association for Public Policy Analysis and Management variables, the choice of how to split the pre-treatment periods into training and validation periods, and even the choice of software and data-sorting criteria (see Klößner et al, 2017, for details on this last point). Therefore, our results should be seen as a lower bound on the possibilities for specification searching in SC applications.…”
mentioning
confidence: 99%
“…In a second step, the just-selected V is used as an input to find a new set of optimal country weights W that minimises the differences in predictor variables between the treated unit and its synthetic control over the validation period. In spite of some concerns with this approach (seeKlößner et al, 2017), we have also run, as a robustness check, all our synthetic control experiments using cross-validation. The estimated FCL effects are broadly similar to those presented in Sections 4.3.1 and 4.3.2.…”
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confidence: 99%
“…As Klößner, Kaul, Pfeifer, and Schieler () show, one should be careful with interpreting such v weights with respect to “importance” since they are not uniquely defined. If we follow M. Becker, Klößner, and Pfeifer () and apply a cross‐validation to determine predictor weights v, we arrive at results fully in line with our approach here.…”
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confidence: 99%