title: 'Gravity: Estimation Methods for Gravity Models in R' authors: - affiliation: 1 name: Anna-Lena Wölwer - affiliation: 1 name: Jan Pablo Burgard - affiliation: 2 name: Joshua Kunst - affiliation: 2 name: Mauricio Vargas orcid: 0000-0003-1017-7574 date: "23 August 2018" output: pdf_document bibliography: REFERENCES.bib tags: - R - econometrics - gravity model - international trade - migration affiliations: - index: 1 name: Trier University - index: 2 name: Pontifical Catholic University of Chile
Gravity models are used to explain bilateral flows related to the sizes of bilateral partners, a measure of distance between them and other influences on interaction costs. The underlying idea is rather simple. The greater the masses of two bodies and the smaller the distance between them, the stronger their attraction. For a state-of-the-art exposition about cross-sectional data see @WoelwerBressleinBurgard2018.
The gravity package provides a wrapper of different standard estimation methods that can be quite difficult to implement in R [@baser]. By considering the descriptions and code of these methods, users get a comprehensive and application-oriented access, can see which methods may be suitable for certain research questions or data types, and can extend the code available for their specific research projects.
The functions included in this package are designed to be consistent with the Stata code used in @Head2014. Beyond offering an rstats open alternative to gravity model estimation in Stata we also provide cross-system compatibility that eases reproducible research for both researchers and students.
The current version of this package relies heavily on the rlang
package [@rlang] which provides
tools to work with the core language features of base R and the tidyverse
package [@tidyverse]. As a
result we provide fast model fitting computation while keeping correct handling and consistency
when facing rank-deficient model matrices that base R handles well.
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