Bidirectional Two-Stage Least Squares Estimation R package BiTSLS version 0.1.0 Implements bidirectional two-stage least squares (Bi-TSLS) estimation for identifying bidirectional causal effects between two variables in the presence of unmeasured confounding. The method uses proxy variables (negative control exposure and outcome) along with at least one covariate to handle confounding. Software Depends: R (>= 3.5.0) Imports: stats Jiaqi Min <fhoneysuckle7@gmail.com> Comprehensive R Archive Network (CRAN) Jiaqi Min [aut, cre] MIT + file LICENSE (https://CRAN.R-project.org/package=BiTSLS/LICENSE) 2025-05-28 application/tgz https://CRAN.R-project.org/package=BiTSLS doi:10.32614/CRAN.package.BiTSLS