matchOnPsAndCovariates uses the provided propensity scores and a set of covariates to match target to comparator persons.

matchOnPsAndCovariates(
population,
caliper = 0.2,
caliperScale = "standardized logit",
maxRatio = 1,
cohortMethodData,
covariateIds
)

## Arguments

population A data frame with the three columns described below. The caliper for matching. A caliper is the distance which is acceptable for any match. Observations which are outside of the caliper are dropped. A caliper of 0 means no caliper is used. The scale on which the caliper is defined. Three scales are supported: caliperScale = 'propensity score', caliperScale = 'standardized', or caliperScale = 'standardized logit'. On the standardized scale, the caliper is interpreted in standard deviations of the propensity score distribution. 'standardized logit' is similar, except that the propensity score is transformed to the logit scale because the PS is more likely to be normally distributed on that scale (Austin, 2011). The maximum number of persons int the comparator arm to be matched to each person in the treatment arm. A maxRatio of 0 means no maximum: all comparators will be assigned to a target person. An object of type cohortMethodData as generated using getDbCohortMethodData. One or more covariate IDs in the cohortMethodData object on which subjects should be also matched.

## Value

Returns a date frame with the same columns as the input data plus one extra column: stratumId. Any rows that could not be matched are removed

## Details

The data frame should have at least the following three columns:

 rowId (numeric) A unique identifier for each row (e.g. the person ID) treatment (integer) Column indicating whether the person is in the target (1) or comparator (0) group propensityScore (numeric) Propensity score

This function implements the greedy variable-ratio matching algorithm described in Rassen et al (2012).

The default caliper (0.2 on the standardized logit scale) is the one recommended by Austin (2011).

## References

Rassen JA, Shelat AA, Myers J, Glynn RJ, Rothman KJ, Schneeweiss S. (2012) One-to-many propensity score matching in cohort studies, Pharmacoepidemiology and Drug Safety, May, 21 Suppl 2:69-80.

Austin, PC. (2011) Optimal caliper widths for propensity-score matching when estimating differences in means and differences in proportions in observational studies, Pharmaceutical statistics, March, 10(2):150-161.

## Examples

# todo