Medicare Current Beneficiary Survey (MCBS)

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The monitoring system for Medicare enrollees in the United States on topics not available in the program’s administrative data, such as out of pocket expenditure and beneficiary satisfaction.

  • Survey and supplemental tables with one row per sampled individual, although downloadable datasets not linkable.

  • A complex sample survey designed to generalize to all elderly and disabled individuals with at least one month of program enrollment during the calendar year.

  • Released annually as a public use file since 2015.

  • Conducted by the Office of Enterprise Data and Analytics (OEDA) of the Centers for Medicare & Medicaid Services (CMS) through a contract with NORC at the University of Chicago.

Download, Import, Preparation

tf <- tempfile()

this_url <- "https://www.cms.gov/files/zip/cspuf2021.zip"

download.file( this_url , tf , mode = 'wb' )

unzipped_files <- unzip( tf , exdir = tempdir() )

mcbs_csv <- grep( '\\.csv$' , unzipped_files , value = TRUE )

mcbs_df <- read.csv( mcbs_csv )

names( mcbs_df ) <- tolower( names( mcbs_df ) )

Save Locally  

Save the object at any point:

# mcbs_fn <- file.path( path.expand( "~" ) , "MCBS" , "this_file.rds" )
# saveRDS( mcbs_df , file = mcbs_fn , compress = FALSE )

Load the same object:

# mcbs_df <- readRDS( mcbs_fn )

Survey Design Definition

Construct a complex sample survey design:

library(survey)

mcbs_design <-
    svrepdesign(
        weight = ~cspufwgt ,
        repweights = 'cspuf[0-9]+' ,
        mse = TRUE ,
        type = 'Fay' ,
        rho = 0.3 ,
        data = mcbs_df
    )

Variable Recoding

Add new columns to the data set:

mcbs_design <-
    update(
        
        mcbs_design ,

        one = 1 ,
        
        csp_age =
            factor( 
                csp_age , 
                levels = 1:3 , 
                labels = 
                    c( 
                        '01: younger than 65' ,
                        '02: 65 to 74' ,
                        '03: 75 or older'
                    )
            ) ,
        
        two_or_more_chronic_conditions = as.numeric( csp_nchrncnd > 1 ) ,

        csp_sex = factor( csp_sex , labels = c( 'male' , 'female' ) )
    )

Analysis Examples with the survey library  

Unweighted Counts

Count the unweighted number of records in the survey sample, overall and by groups:

sum( weights( mcbs_design , "sampling" ) != 0 )

svyby( ~ one , ~ csp_age , mcbs_design , unwtd.count )

Weighted Counts

Count the weighted size of the generalizable population, overall and by groups:

svytotal( ~ one , mcbs_design )

svyby( ~ one , ~ csp_age , mcbs_design , svytotal )

Descriptive Statistics

Calculate the mean (average) of a linear variable, overall and by groups:

svymean( ~ pamtoop , mcbs_design )

svyby( ~ pamtoop , ~ csp_age , mcbs_design , svymean )

Calculate the distribution of a categorical variable, overall and by groups:

svymean( ~ csp_sex , mcbs_design )

svyby( ~ csp_sex , ~ csp_age , mcbs_design , svymean )

Calculate the sum of a linear variable, overall and by groups:

svytotal( ~ pamtoop , mcbs_design )

svyby( ~ pamtoop , ~ csp_age , mcbs_design , svytotal )

Calculate the weighted sum of a categorical variable, overall and by groups:

svytotal( ~ csp_sex , mcbs_design )

svyby( ~ csp_sex , ~ csp_age , mcbs_design , svytotal )

Calculate the median (50th percentile) of a linear variable, overall and by groups:

svyquantile( ~ pamtoop , mcbs_design , 0.5 )

svyby( 
    ~ pamtoop , 
    ~ csp_age , 
    mcbs_design , 
    svyquantile , 
    0.5 ,
    ci = TRUE 
)

Estimate a ratio:

svyratio( 
    numerator = ~ pamtoop , 
    denominator = ~ pamttot , 
    mcbs_design 
)

Subsetting

Restrict the survey design to household income below $25,000:

sub_mcbs_design <- subset( mcbs_design , csp_income == 1 )

Calculate the mean (average) of this subset:

svymean( ~ pamtoop , sub_mcbs_design )

Measures of Uncertainty

Extract the coefficient, standard error, confidence interval, and coefficient of variation from any descriptive statistics function result, overall and by groups:

this_result <- svymean( ~ pamtoop , mcbs_design )

coef( this_result )
SE( this_result )
confint( this_result )
cv( this_result )

grouped_result <-
    svyby( 
        ~ pamtoop , 
        ~ csp_age , 
        mcbs_design , 
        svymean 
    )
    
coef( grouped_result )
SE( grouped_result )
confint( grouped_result )
cv( grouped_result )

Calculate the degrees of freedom of any survey design object:

degf( mcbs_design )

Calculate the complex sample survey-adjusted variance of any statistic:

svyvar( ~ pamtoop , mcbs_design )

Include the complex sample design effect in the result for a specific statistic:

# SRS without replacement
svymean( ~ pamtoop , mcbs_design , deff = TRUE )

# SRS with replacement
svymean( ~ pamtoop , mcbs_design , deff = "replace" )

Compute confidence intervals for proportions using methods that may be more accurate near 0 and 1. See ?svyciprop for alternatives:

svyciprop( ~ two_or_more_chronic_conditions , mcbs_design ,
    method = "likelihood" )

Regression Models and Tests of Association

Perform a design-based t-test:

svyttest( pamtoop ~ two_or_more_chronic_conditions , mcbs_design )

Perform a chi-squared test of association for survey data:

svychisq( 
    ~ two_or_more_chronic_conditions + csp_sex , 
    mcbs_design 
)

Perform a survey-weighted generalized linear model:

glm_result <- 
    svyglm( 
        pamtoop ~ two_or_more_chronic_conditions + csp_sex , 
        mcbs_design 
    )

summary( glm_result )

Replication Example

This example matches the weighted total from the 2021 Data User’s Guide: Cost Supplement File Public Use File:

stopifnot( round( coef( svytotal( ~ one , mcbs_design ) ) , 0 ) == 59040948 )

Analysis Examples with srvyr  

The R srvyr library calculates summary statistics from survey data, such as the mean, total or quantile using dplyr-like syntax. srvyr allows for the use of many verbs, such as summarize, group_by, and mutate, the convenience of pipe-able functions, the tidyverse style of non-standard evaluation and more consistent return types than the survey package. This vignette details the available features. As a starting point for MCBS users, this code replicates previously-presented examples:

library(srvyr)
mcbs_srvyr_design <- as_survey( mcbs_design )

Calculate the mean (average) of a linear variable, overall and by groups:

mcbs_srvyr_design %>%
    summarize( mean = survey_mean( pamtoop ) )

mcbs_srvyr_design %>%
    group_by( csp_age ) %>%
    summarize( mean = survey_mean( pamtoop ) )