In Song Kim, Erik Wang and Kosuke Imai. ''PanelMatch: Matching Methods for Causal Inference with Time-Series Cross-Section Data.'' available through GitHub repository.

In Song Kim and Kosuke Imai. ''wfe: Weighted Linear Fixed Effects Regression Models for Causal Infernece.'' available through The Comprehensive R Archive Network.

In Song Kim, Steven Liao, and Kosuke Imai. ''dynCluster: Dynamic Clustering Algorithm.'' available through Github repository.

Feng Zhu and In Song Kim. ''concordance: Concordance Utilities for International Trade Research.'' available through The Comprehensive R Archive Network. [bibtex]

Concordance across different nomenclatures has become essential for researchers conducting product-level analysis. The package currently supports concordance across various versions of Harmonized System (HS), Standard International Trade Classification (SITC), Broad Economic Categories (BEC), North American Industry Classification System (NAICS), and Standard Industrial Classification (SIC). Please contact me if you are interested in contributing to the package so that the package can cover a wider range of nomenclatures.