### R

- MatchIt http://gking.harvard.edu/matchit
- Ho, D.E., Imai, K., King, G., and Stuart, E.A. (2011). MatchIt: Nonparametric preprocessing for parameteric causal inference.
*Journal of Statistical Software*42(8). http://www.jstatsoft.org/v42/i08 - Two-step process: does matching, then user does outcome analysis (integrated with Zelig package for R)
- Wide array of estimation procedures and matching methods available: nearest neighbor, Mahalanobis, caliper, exact, full, optimal, subclassification
- Built-in numeric and graphical diagnostics
- Matching http://sekhon.berkeley.edu/matching
- Sekhon, J. S. (2011). Multivariate and propensity score matching software with automated balance optimization:
The Matching package for R.
*Journal of Statistical Software*42(7). http://www.jstatsoft.org/v42/i07 - Uses automated procedure to select matches, based on univariate and multivariate balance diagnostics
- Primarily 1:M matching (where M is a positive integer), allows matching with or without replacement, caliper, exact
- Includes built-in effect and variance estimation procedures
- twang http://cran.r-project.org/web/packages/twang/index.html
- Ridgeway, G., McCaffrey, D., and Morral, A. (2006). twang: Toolkit for weighting and analysis of nonequivalent groups.
- Functions for propensity score estimating and weighting, nonresponse weighting, and diagnosis of the weights
- Primarily uses generalized boosted regression to estimate the propensity scores
- cem http://gking.harvard.edu/cem/
- Iacus, S.M., King, G., and Porro, G. (2008). Matching for Causal Inference Without Balance Checking. Available here.
- Implements coarsened exact matching
- Can also be implemented through MatchIt
- optmatch http://cran.r-project.org/web/packages/optmatch/index.html
- Hansen, B.B., and Fredrickson, M. (2009). optmatch: Functions for optimal matching.
- Variable ratio, optimal, and full matching
- Can also be implemented through MatchIt
- PSAgraphics http://cran.r-project.org/web/packages/PSAgraphics/index.html
- Helmreich, J.E. and Pruzek, R.M. (2009). PSAgraphics: An R Package to Support Propensity Score Analysis.
*Journal of Statistical Software*29(6). Available here. - From webpage: "A collection of functions that primarily produce graphics to aid in a Propensity Score Analysis (PSA). Functions include: cat.psa and box.psa to test balance within strata of categorical and quantitative covariates, circ.psa for a representation of the estimated effect size by stratum, loess.psa that provides a graphic and loess based effect size estimate, and various balance functions that provide measures of the balance achieved via a PSA in a categorical covariate."
- Synth
- Abadie, A., Diamond, A., and Hainmueller, H. (2011). Synth: An R Package for Synthetic Control Methods in Comparative Cast Studies.
*Journal of Statistical Software*42(13). http://www.jstatsoft.org/v42/i13 - Implements weighting approach to creating synthetic control groups
- Useful when there is a single treated unit, such as a state or country. Main idea is to form a weighted average of comparison units that, when weighted, looks like the treated unit.

- Abadie, A., Diamond, A., and Hainmueller, H. (2011). Synth: An R Package for Synthetic Control Methods in Comparative Cast Studies.

### Stata

- psmatch2 http://ideas.repec.org/c/boc/bocode/s432001.html
- Leuven, E. and Sianesi, B. (2003). psmatch2. Stata module to perform full Mahalanobis and propensity score matching, common support graphing, and covariate imbalance testing.
- Allows k:1 matching, kernel weighting, Mahalanobis matching
- Includes built-in diagnostics
- Includes procedures for estimating ATT or ATE
- pscore http://www.lrz-muenchen.de/~sobecker/pscore.html
- Becker, S.O. and Ichino, A. (2002). Estimation of average treatment effects based on propensity scores (2002)
*The Stata Journal*2(4): 358-377. - k:1 matching, radius (caliper) matching, and stratification (subclassification)
- For estimating the ATT
- match http://www.economics.harvard.edu/faculty/imbens/software_imbens
- Abadie, A., Drukker, D., Herr, J. L., and Imbens, G. W. (2004). Implementing matching estimators for average treatment effects in Stata.
*The Stata Journal*4(3): 290-311. Available here. - Primarily k:1 matching (with replacement)
- Allows estimation of ATT or ATE, including robust variance estimators
- cem http://gking.harvard.edu/cem/
- Iacus, S.M., King, G., and Porro, G. (2008). Matching for Causal Inference Without Balance Checking. Available here.
- Implements coarsened exact matching

### SAS

- SAS usage note: http://support.sas.com/kb/30/971.html
- Local and global optimal propensity score matching
- Coca-Perraillon, M. (2007). Local and global optimal propensity score matching. In SAS Global Forum 2007. Paper 185-2007. Available here.
- Variety of matching methods. No built in diagnostics. Assumes propensity score already estimated.
- Greedy matching (1:1 nearest neighbor)
- Parsons, L. S. (2001). Reducing bias in a propensity score matched-pair sample using greedy matching techniques. In SAS SUGI 26, Paper 214-26. Available here.
- Parsons, L.S. (2005). Using SAS software to perform a case-control match on propensity score in an observational study. In SAS SUGI 30, Paper 225-25. Available here.
- Kosanke, J., and Bergstralh, E. (2004). gmatch: Match 1 or more controls to cases using the GREEDY algorithm. http://www.mayo.edu/research/departments-divisions/department-health-sciences-research/division-biomedical-statistics-informatics/software/locally-written-sas-macros
- 1:1 Mahalanbois matching within propensity score calipers
- Feng, W.W., Jun, Y., and Xu, R. (2005). A method/macro based on propensity score and Mahalanobis distance to reduce bias in treatment comparison in observational study. www.lexjansen.com/pharmasug/2006/publichealthresearch/pr05.pdf
- Weighting
- Leslie, S. and Thiebaud, P. (2006). Using propensity scores to adjust for treatment selection bias. http://www.lexjansen.com/wuss/2006/Analytics/ANL-Leslie.pdf
- Variable ratio matching, optimal matching algorithm
- Kosanke, J., and Bergstralh, E. (2004). Match cases to controls using variable optimal matching. http://www.mayo.edu/research/departments-divisions/department-health-sciences-research/division-biomedical-statistics-informatics/software/locally-written-sas-macros

### SPSS

- Propensity score matching in SPSS http://arxiv.org/ftp/arxiv/papers/1201/1201.6385.pdf
- Thoemmes, F. (2012). Propensity score matching in SPSS. http://sourceforge.net/projects/psmspss/files/
- Nearest neighbor propensity score matching with various options (with/without replacement, calipers, k to 1, etc.)
- Detailed balance statistics and graphs
- Actually calls MatchIt using a point and click interface

### Software for performing analyses of sensitivity to an unobserved confounder

- R
- rbounds: An R package for sensitivity analysis with matched data (L. Keele). http://www.personal.psu.edu/ljk20/rbounds.html
- sensitivity function in twang package (G. Ridgeway et al.). http://rss.acs.unt.edu/Rdoc/library/twang/html/sensitivity.html
- Stata
- rbounds: Stata module to perform Rosenbaum sensitivity analysis for average treatment effects on the treated (M. Gangl) http://econpapers.repec.org/software/bocbocode/s438301.htm
- sensatt: A simulation-based sensitivity analysis for matching estimators (T. Nannicini) http://www.tommasonannicini.eu/Portals/0/sensatt_wp_4.pdf
- Nannicini T. (2007). A Simulation-Based Sensitivity Analysis for Matching Estimators. Stata Journal, 7(3), 334-350
- Ichino A., Mealli F., Nannicini T. (2008). From Temporary Help Jobs to Permanent Employment: What Can We Learn from Matching Estimators and their Sensitivity? Journal of Applied Econometrics, 23(3), 305-327.
- Excel
- Love, T.E. (2008) Spreadsheet-based sensitivity analysis calculations for matched samples. Center for Health Care Research & Policy, Case Western Reserve University. http://www.chrp.org/propensity/, http://www.chrp.org/propensity/sensitivitydocumentation.pdf, http://www.chrp.org/propensity/sensitivityspreadsheet.xls