## Appendix

Table 1. The candidate features.

Category	Features
Patient demographics features	Age; gender; race; ethnicity (Hispanic or non-Hispanic); marital status (divorced, married, partnered, separated, single, or widowed); language; and religion.
Features reflecting properties of the area related to the five-digit zip code of the patient’s home address	The area’s population size; black population percentage; Hispanic population percentage; white population percentage; estimated number of households; average house value; average household income; estimated average number of people per household; average elevation; and the 2003 rural-urban continuum code, which is a number between 1 (most urban) and 9 (most rural) reflecting rurality [37]. Except for the last two, all of these features were derived from 2010 census data.
Features reflecting properties of the census block group where the patient resides	The block group’s number of employed people 16 and older; percentage of employed people 16 and older in a white-collar occupation; percentage of households with >1 person per room; percentage of households that are owner-occupied; percentage of single-parent households with dependents <18 years old; percentage of occupied housing units without complete plumbing; percentage of households without a phone; percentage of households without a motor vehicle; income disparity measure = log(the number of households with median income < US $15,000 / the number of households with median income > US $75,000); number of civilian labor force 16 and older; median family income; median home value; median monthly mortgage payment; median monthly rent payment; percentage of families below 150% of the federal poverty level; percentage of families below the federal poverty level; percentage of population 25 and older with < 9 years of education; percentage of population 25 and older with a high school diploma or higher education; combined population of each of the census blocks within the block group that qualifies as rural under the 2013 US Census; number of families; number of households; number of occupied households; size of the population 25 and older; population size; number of single-parent households; percentage of the civilian labor force 16 and older that is unemployed; combined population of each of the census blocks within the block group that qualifies as urban under the 2013 US census; national health literacy score developed by the University of North Carolina at Chapel Hill [38]; Singh’s area deprivation index measuring the neighborhood’s socioeconomic deprivation [39]; indicator of whether the urban population is larger than the rural population; and rural/urban status (rural, urban, or mixed urban/rural). Except for the last four, all of these features were based on the US Census 2013 American Community Survey five- year rolling averages. The last three features were based on 2013 US census data.
Laboratory test-related features	The number of laboratory tests; the number of laboratory tests with abnormal results; the number of days since having the last laboratory test; the maximum blood eosinophil count; the maximum percentage of blood eosinophils; the maximum total