Study Setting and Data Sources
The study was a retrospective in nature which was conducted using data obtained from multiple sources. The primary data source was the medical insurance claims data from 2013 to 2016 obtained from Texas Children’s Health Plan (TCHP), a Houston based pediatric Medicaid managed care program that offers Medicaid and Children’s Health Insurance Program (CHIP) in more than 20 counties of Southeast Texas. In Texas, 40% of children below age 21 are covered by Medicaid and CHIP. (20) TCHP data included characteristics of providers who were actively serving the TCHP enrollees, medical claim details of enrollees and enrollees’ characteristics (date of birth, gender, race/ethnicity) and zip code of the enrollees’ residence. Zip code of enrollees’ residence was used to ascertain the location of study population.
Using zip code of the enrollees’ residence, the data was also linked to 2010 US Census data to identify the neighborhood related information of the study population and geodata of the study area.(21)
The data was further linked with the National Provider Identifier (NPI) Registry to ascertain provider’s primary practice location.22) This study only included those PCPs who had provided at least one service to the TCHP pediatric enrollees in a year.
Study Population
The study period was between January 2013 and December 2016. As children and adolescents could receive behavioral health screening multiple times during the four years of study period, we created three distinct study periods (2013-14, 2014-15, and 2015-16) for the calculation of behavioral health screening rate. A study period constituted of two years, first year was defined as a wash-out period and second year was defined as a measurement period. Inclusion criteria used in the study were (a) had at least 10 months of enrollment in both measurement period and washout period; b) had absence of mental disorder diagnosis or treatment during the washout period; and c) age of enrollees between 4- and 18-years during measurement period. Enrollees were allowed to be included in multiple study periods based on if they met the inclusion criteria of more than one study period.
Dependent Variable/Outcome Measure
Behavioral health screening
Individuals having at least one CPT® (Current Procedural Terminology)/HCPCS (Healthcare Common Procedure Coding System) code of behavioral health screening (reported in appendix) during the measurement period were considered as screened individuals. In case of those individuals who also received mental health services other than screening during the measurement period, only those who received screening prior to the first visit relevant to any other mental health services were considered as screened. The yearly screening rates was calculated as total screened in the measurement period divided by the number of eligible individuals in a given study period.
Main Independent Variables
Geographic access measures
Geographic accessibility (one-way travel distance to PCP) and geographic availability (PCP density per 10,000 residents) were geographic access measures used in the study. The PCPs included in the study were physicians with specialty of family medicine, general practice, internal medicine, pediatrics or adolescent medicine, nurse practitioners (adult and pediatric), and physician assistants.
One-travel distance to the nearest PCP (geographic accessibility)
The one-way travel distance to the nearest PCP was measured for each individual identified. Travel distance was defined as the shortest route by a car (different from straight-line distance between two points) from the geocode of enrollees’ residence zip code to geocode of provider’s practice locations. To calculate the one-way travel distance, first step was to geo-locate the population weighted center of zip code tabulation area (ZCTA) by geo-averaging the geocodes of all the population center of census blocks that were within the boundary of zip code tabulation area while using the population of census block as a weight.(23) This exercise was conducted on ArcGIS using the geo-information (maps) provided by UScensus.gov. The second step was to assign a geocode to each provider’s practice locations (street address). Lastly, the travel distance between two points was estimated using a SAS® algorithm that calculates the shortest route possible between two locations based on average speed and the maximum speed limit of the road obtained from Google Map®. (24)
PCP Density per 10,000 residents within 10-mile travel distance (geographic availability)
PCP density per 10,000 residents within 10-mile travel distance of enrollees’ residence was used to measure geographic availability of PCPs. A 10-mile distance was chosen for this measure based on an assumption that anything within travel distance of 10-mile of enrollees could be considered as vicinity to enrollees. It was calculated using the geographic information system-based floating catchment method.(25) This method identify provider to population ratio within a pre-determined (say 10 mile) travel distance circle (called as catchment area) around enrollee’s residence. This method handles the issue of border crossing in aggregate measure such as “provider to population ratio within a zip code”, while being still easy to understand.
The measure was calculated by dividing count of PCPs within 10-mile travel distance from the population weighted center of zip code of enrollees’ residence by the census population within the 10-mile radius of that zip code. First step was to determine the count of PCPs within 10-mile travel distance of enrollees. To calculate travel distance between providers and enrollees’ zip code, same method was applied as described in travel distance to nearest PCP measure earlier in the study. After that, count of PCPs within 10-mile travel distance radius was computed for each enrollees’ zip code. Second step was to calculate the population within 10-mile radius from population center of zip code. For this, number of census blocks that were partial or completely part of 10-mile radius circle were identified.(26) Census block population was attributed to the catchment’s population based on extent they were the part of 10-mile radius circle. For instance, if the 0.5 census block coincides the 10-mile radius circle then only half of the population of census block was used for the calculation of circle’s population.
The sub-cohort of study population that had at least one PCP within 10 mile of travel distance, were categorized into following subcategories based on the empirical distribution of the data: ≤2 PCPs; 2.1-5 PCPs; 5.1-10 PCPs; >10 PCPs
Enrollees’ race/ethnicity
Whites, Blacks, Hispanics, Others (Asian, American Indians; Pacific Islanders; other races) and unknown were the categories of race/ethnicity included in the study.
Covariates
Other variables controlled in the study were demographics of individuals (age, gender, and Medicaid eligibility categories), neighborhood poverty level, and urban influence.
Age of enrollees were categorized into three categories 4-6 years; 7-12 years; and 13-18 years. Medicaid eligibility of the study population were of two types: CHIP (family income above poverty level) and STAR (family income below poverty level).(27, 28) Therefore, Medicaid’s eligibility could be assumed proxy measure for family poverty level.
Neighborhood poverty level was calculated based on the percentage of households living below poverty level in enrollee’s zip code provided by US Census data.(29) Urban influence was categorized based on the Urban Influence Code 2013, divided as those living in large metro (area of 1+million residents); or those who are living adjacent to large metro; and those living in small metro (area of <1 million residents) or adjacent to small metro.(30)
Statistical Analysis
The study has evaluated the association of primary independent measure (geographic access measures, race/ethnicity, and the interaction between geographic access measures and race/ethnicity) with the likelihood of receiving behavioral health screening using multivariable logistic regression.(31) Because, the study included both individual-level and zip code-level variables, we first utilized two-level model where zip code was at higher level and individuals were nested within the zip codes. Intraclass correlation was used to assess the performance of zip code as a higher level in explaining the variation which was only 5% for the empty two-level model.(32) Based on that one-level model was used in which zip code level variables and individual level variable were at one level.
ArcGIS® was used for all geographic information system functions, except travel distance that was calculated using Google Map®. All statistical analyses were carried out using SAS®. This study was approved by our University Institutional Review Board.