Article pdf available in stata journal 98 january 2010 with 973 reads. This paper introduces a stata implementation of coarsened exact matching cem, a new method for improving the estimation of causal effects by reducing imbalance in covariates between treated and control groups. Coarsened exact matching is faster, is easier to use and understand, requires fewer assumptions, is more easily automated, and possesses more attractive statistical properties for many applications than do existing matching methods. The program implements the coarsened exact matching cem algorithm described in. Cem is faster, easier to use and understand, requires fewer assumptions, more easily automated, and possesses more attractive statistical properties for many applications than existing matching methods. Apr 19, 2017 a member is represented by properties coarsened to discrete values using a coarsening or binning strategy. Hth david sent with verizon mobile email original message from. This paper introduces a stata implementation of coarsened exact matching. Coarsened exact matching cem offers an alternative solution, which is faster and easier to understand. This paper introduces a stata implementation of coarsened exact matching cem, a. Reducing bias in a propensity score matchedpair sample using greedy matching techniques.
Gary king of harvard university offers a different take on matching procedures by means of a new technique known as coarsened exact matching cem. Once all five are downloaded, users can generate the following. In coarsened exact matching, users temporarily coarsen their data, exact match on these coarsened data, and then. Causal effect of selfesteem on cigarette smoking stages in.
This paper introduces a stata implementation of coarsened exact matching cem, a new method for improving the estimation of causal effects by reducing imbalance in co. Exact matching on discrete covariates and ra with fully interacted discrete covariates perform the same nonparametric estimation. Coarsened exact matching is faster, is easier to use and understand, requires fewer assumptions. Coarsened exact matching and multivariate matching methods that are monotonic imbalance bounding. The goal of the original study was to estimate the effect of a job training program the variable treated on real earnings in 1978 the variable re78. A member is represented by properties coarsened to discrete values using a coarsening or binning strategy. My first step was to match the groups across a number of variables age, sex, preopasa, premob, and origin using the cem package for coarsened exact matching. Causal effect of selfesteem on cigarette smoking stages. Coarsened exact matching in stata stata journal, 2009, with matthew blackwell, cem.
Coarsened exact matching for stata matthew blackwell institute for quantitative social science harvard university joint work with stefano m. Coarsened exact matching is faster, is easier to use and understand, requires fewer assumptions, is more easily automated, and possesses more attractive statistical. Exact matching dear statalist members, i am trying to run a coarsened exact matching to create comparable pair of individuals within my sample. Two roads diverged in a narrow datasetwhen coarsened exact. In this case, the algorithm outputs the same matching solution for each multiply imputed data set i. We discuss a method for improving causal inferences called coarsened exact matching cem, and the new monotonic imbalance bounding mib class of matching methods from which cem is derived. Two roads diverged in a narrow datasetwhen coarsened. This option will delete some data that matched well, and thus likely increase the variance, but it means that subsequent analyses do not require weights. Iacus, gary king, and giuseppe porro, causal inference without balance checking. Coarsened exact matching political analysis, 2012 and multivariate matching methods that are monotonic imbalance bounding jasa, 2011, cem. Other matching methods inheret many of cems properties when applied to. Abstract this paper introduces a stata implementation of coarsened exact matching cem, a new method for improving the estimation of causal effects by reducing imbalance in covariates between treated and control groups. Other matching methods inherit many of the coarsened exact matching methods properties when applied to further match data preprocessed by coarsened exact matching.
Download fulltext pdf download fulltext pdf download fulltext pdf download fulltext pdf. Harvard university statistical software components from boston college department of economics. Another approach you might consider is using coarsened exact matching, cem, a user written program found on ssc ssc install cem using. Coarsened exact matching in stata gary king harvard. The cem command implements the coarsened exact matching algorithm in stata. In cem, users temporarily coarsen their data, exact match on these coarsened data, then run their analysis on the uncoarsened, matched data.
This algorithm, and its statistical properties, are described in stefano m. However when i come to running the command i am faced with the. Cem may be used alone or in combination with any existing matching method. I have eliminated nas and am running matching on polity2 7 treatment. I am trying to run coarsened exact matching on a dataset of 6549 observations and 94 variables. We started with the procedure of coarsened exact matching to identify poes that more closely resemble the soes in the database both.
Coarsened exact matching cem on panel data statalist. We summarize what is known about cem and mib, derive and illustrate several new desirable statistical. Coarsened exact matching coarsened exact matching cem is a monotonoic imbalance bounding mib matching method which means that the balance between the treated and control groups is chosen by the user ex ante rather than discovered through the usual laborious process of checking after the fact and repeatedly reestimating, and so that adjusting the imbalance on one variable has no effect. Ricardo, the first thing you would need to do is to generate a variable that indicates whether a firm was involved in an acquisition. The cem package provides a stata implementation of coarsened exact matching, a new method for improving the estimation of causal effects by reducing imbalance in covariates between.
Matthew blackwell, stefano iacus, gary king and giuseppe porro additional contact information matthew blackwell. Coarsened exact matching cem is a monotonoic imbalance bounding mib matching method which means that the balance between the treated and control groups is chosen by the user ex ante rather than discovered through the usual laborious process of checking after the fact and repeatedly reestimating, and so that adjusting the imbalance on one. Coarsened exact matching in stata matthew blackwell1 stefano iacus2 gary king3 giuseppe porro4 february 22, 2010 1institute for quantitative social science,1737 cambridge street, harvard university, cam bridge ma 028. This function transforms a typical cem matching solution to a ktok match, with k variable along strata. Coarsened exact matching explained devmotivation medium. This option will delete some data that matched well, and thus likely increase the variance, but it means that subsequent. A coarsened exact matching approach this paper is the first to use the method of coarsened exact matching cem to estimate the impact of mood disorders on medical care costs in order to address the endogeneity of mood disorders. For instance, adding one continuous variable to a dataset e ectively kills exact matching since two observations. Nearest neighbor, radius, coarsened exact, percentile rank and mahalanobis and euclidean distance matching. It implements an efficient method for distance based matching preventing the inflationary increment of the runtime. Collapsing categories or cutting up discrete covariates performs the same function as a bandwidth in nonparametric kernel regression. Propensity score matching psm is the older, more established technique in the literature. The stata blog exact matching on discrete covariates is the.
The most common matching technique, propensity score matching, however, is slow and difficult to apply. Matthew blackwell harvard university stefano iacus university of milan gary king harvard university giuseppe porro university of trieste. The program implements the coarsened exact matching cem. Aug 16, 2016 exact matching on discrete covariates and ra with fully interacted discrete covariates perform the same nonparametric estimation. Exploring robust methods for evaluating treatment and. One approach to impact evaluation is the use of coarsened exact matching, a statistical technique that allows researchers to compare program participants to nonparticipants, controlling for factors believed to influence outcomes of interest. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Coarsened exact matching is faster, is easier to use and understand, requires fewer assumptions, is more easily automated, and. Coarsened exact matching in stata matthew blackwell. How to use cem for spss in order to demonstrate the syntax of cem in spss, you can download an example dataset of a job training program. In this article, we introduce a stata implementation of coarsened exact matching, a new method for improving the estimation of causal effects by.
Iacus, gary king, and giuseppe porro, matching for causal inference without balance checking. Using sas software to perform a casecontrol match on propensity score in an. Coarsened exact matching cem package in stata statalist. Cem is a nonparametric matching method widely used by researchers to avoid the confounding influence of pretreatment control variables to improve causal inference in quasiexperimental studies.
We address the possibility of unobserved selfselection into exit mode by using coarsened exact matching, and in two additional ways. The cem package provides a stata implementation of coarsened exact matching, a new method for improving the estimation of causal effects by reducing imbalance in covariates between treated and control groups. Comparison of matching metrics and causal effects estimated from coarsened exact matching cem and propensity score matching psm effectiveness of two matching methodologies based on the qualitative and quantitative imbalance results observed in tables 1 and and2, 2, cem and psm were employed within the aforementioned sampling design. Cem via the dialog menu in order to demonstrate the syntax of cem in spss, you can download an example dataset of a job training program. The goal of the original study was to estimate the. In this article, we introduce a stata implementation of coarsened exact matching, a new method for improving the estimation of causal effects by reducing imbalance in covariates between treated and control groups. The cem package provides a stata implementation of coarsened exact matching, a new method for improving the. Iacus and gary king and nathaniel beck and matt blackwell and andy eggers and adam glynn and justin grimmer and jens hainmueller and ben hansen and kosuke imai and guido imbens and fabrizia mealli, title causal inference without balance checking. Coarsened exact matching coarsened exact matching cem is a monotonoic imbalance bounding mib matching method which means that the balance between the treated and control groups is chosen by the user ex ante rather than discovered through the usual laborious process of checking after the fact and repeatedly reestimating, and so that. Another alternative is the coarsened exact matching procedure of blackwell et al. Students were matched based on coarsened exact matching on pretreatment variables, including age, gender, smoking stages at the first wave of study, socioeconomic status, general risktaking behavior, having a smoker in the family, having a smoker friend, attitude toward smoking, and selfinjury, to ensure statistically equivalent comparison. Coarsened exact matching cem is a relatively new causal inference technique that allows the researcher to nonparametrically create a matched dataset to evaluate the effect of a treatment. To enable construction of a survival curve, matching on age, gender, systolic bp, bmi, and smoking was done using coarsened exact matching.
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