Block Designs for Observational Studies R package observationalBlocks version 1.0.0 Creates block designs of fixed size J with at least one treated and control unit per block. Blocks larger than pairs better distinguish effects caused by a treatment from unmeasured confounding in assignment of individuals to treatment. Somewhat counterintuitively, blocks larger than pairs can use more units while attaining better covariate balance and block homogeneity. A forthcoming manuscript by Brumberg and Rosenbaum details the design. Software Depends: R (>= 3.5.0) Imports: iTOS, lpSolve, stats Suggests: DOS2, sensitivity2x2xk, sensitivitymv, weightedRank, xtable, testthat (>= 3.0.0) Katherine Brumberg <kbrum@umich.edu> Comprehensive R Archive Network (CRAN) Katherine Brumberg [aut, cre] (ORCID: <https://orcid.org/0000-0002-5193-6250>), Paul Rosenbaum [aut] GPL-2 2026-04-10 application/tgz https://CRAN.R-project.org/package=observationalBlocks doi:10.32614/CRAN.package.observationalBlocks