RUCA Version 1.11
RUCA ZIP Code Approximation Methodology
Because the smallest geographic identifiers available for most health care data sets are ZIP codes, a ZIP code approximation of the Census tract-based RUCA codes was developed. The ZIP code approximation is based on the Census tract codes and are not based on commuting data unique to the ZIP code geographic unit.
The RUCA ZIP code approximation was the result of the following analytical steps:
1. 1998 residential and commercial ZIP code information were obtained from Claritas Inc.
2. A ZIP/Census tract crosswalk file from Claritas Inc. identified their 1998 estimates of the populations of all ZIP and Census tract segments. For instance, a ZIP code area might have its boundaries crossed by four Census tracts. For such a ZIP code, the file would contain a population estimate for each of the four segments.
3. Each Census tract was assigned a RUCA code as explained in the section on Census tract RUCA methodology.
4. A file was created where each residential ZIP code had its estimated segment populations aggregated by RUCA code. For example, if a ZIP code area had four Census tract segments each of which had a population of 4000 and two of them were RUCA Census tract assigned 1.0, one was assigned 1.1, and one was assigned 2.0, the file would show ZIP code number, 8000 population for 1.0, 4000 population for 1.1, 4000 population for 2.0, zero population for 2.1, zero population for 2.2, and zero for each of the remaining rubrics.
5. A RUCA assignment algorithm was developed that assigned each ZIP code a RUCA code based on the distribution of its population across the RUCA codes. A clear example would be a ZIP code in which 95 percent of the population was a RUCA code 7.0 and 5 percent was a RUCA code 8.0 – wherein the ZIP would be assigned as a 7.0. The assignment algorithm was developed through trial and error and progressively developed assignment rule by assignment rule. A retrospective combining of the rules would reduce their number, although the order often deliberately assures that a more appropriate code is assigned.
The assignment algorithm consisted of the following rules (the rules are in order and once a ZIP is assigned with a rule it is not considered further):
- if one code (x.x) represent 66.67% or more of the population, it is assigned
- if all the codes of a number type (i.e., 1s = 1.0 and 1.1, 2s, 4s etc.) represent 66.67 of the population, the larger of the subcodes is assigned (e.g., 1.0)
- if 1.0 + 1.1 + 2.0 + 2.1 + 2.2 represent 66.7% or more of the population, the larger of the subcodes is assigned
- if 1.0 + 1.1 + 2.0 + 2.1 + 2.2 represents 50.0% or more of the population and no other code represents more than 40.0% of the population and 4.1 + 5.1 + 7.1 + 8.1 + 10.1 represents more than 20.0% of the population, then assign the larger of codes 1.1, 1.1, 2.0, 2.1, or 2.2
- if the 4s + 5s + 6s or the 7s + 8s + 9s either represent 66.7% or more of the population, then assign the largest of the codes (i.e., largest of the x.x codes from among the 4/5/6 group)
- if the maximum x.x code represents more than 50.0% of the population, assign it
- A few of the residential ZIPs with population (0.6%) remained unassigned after the preceding six assignment rules were implemented. These ZIPs were quite unique in their RUCA Census tract configurations and it was deemed prudent to hand assign them. Dr. Hart assigned each of these ZIP codes a RUCA (twice and then adjudicated the few conflicts) and Dr. Morrill reviewed the assignment rules and the hand assignments logic. In many of the hand assignments, the assignment was clear. For instance, in the case of ZIP code 17022, population was distributed as follows: 1.0, 12.8% (RUCA, % of ZIP population); 2.0, 0.6%; 2.2, 44.4%; and 7.1, 42.3%. RUCA code 2.2 was assigned to the ZIP because 57.8% of the population were in clearly urban areas (1s and 2s) and the 42% that had a primary work commuting relationship with a town of from 2,500-10,000 also had a secondary commuting flow to an urban center. For other ZIPs, the assignment was very difficult because of odd amalgamations of RUCA code population. For example, in rare instances, ZIP code areas moved from the edge of an Urbanized Area outward radially and encompassed many different codes ranging across the rural-urban spectrum. In these troublesome cases, assignment was shaded toward urban (i.e., given a problematic assignment decision between two codes, the more urban one was assigned).
6. Commercial ZIP codes were assigned the RUCA of the most appropriate residential ZIP code based on a Claritas Inc. file (e.g., a commercial ZIP that was surrounded by a residential ZIP was assigned the residential ZIP RUCA).
7. Because the Census tract RUCA assignments were based on 1990 Census Bureau data and the ZIP information and population were based on 1998 ZIP codes and population estimates, there were some loose ends related to ZIPs that had no population and a few other peculiarities (0.5% of the ZIP assignments and a negligible percentage of the population). In each case, assignments were made that were based on geographically contiguous areas.
8. Six ZIP code areas cross state lines. The RUCAs were assigned to each of these ZIPs for the total ZIP code area (i.e., the portions combined from the two states). However, the ZIPs are split in the data files available on this web site.
9. The ZIP code approximation RUCAs are being used in several contexts and match extremely well with the ZIP codes from various data sources (e.g., HCFA claims data ZIP codes). ZIP codes from outside 50 states and District of Columbia do not match and ZIP codes that are not legitimate do not match (e.g., errors in reported ZIP codes and, in a few instances, ZIP codes that are not United States Postal Service standard that are only being used locally).
Assignment Statistics
The results of the RUCA ZIP code approximation assignments by RUCA code are as follows:
Table 1
Population Distribution Across the RUCA codes
| RUCA Codes (v. 1.1) | ZIP RUCA
% Est. 1998 Population |
Census Tract RUCA
% Est. 1998 Population |
Census Tract RUCA
% 1990 Population |
|---|---|---|---|
| 1.0
1.1 2.0 2.1 2.2 3.0 4.0 4.1 5.0 5.1 6.0 7.0 7.1 7.2 7.3 7.4 8.0 8.1 8.2 8.3 8.4 9.0 9.1 9.2 10.0 10.1 10.2 10.3 10.4 10.5 Total** |
64.8
1.3 8.4 .1 .4 .3 6.9 1.0 2.2 .2 .3 2.7 .6 .1 1.8 1.0 .7 .1 .0* .7 .5 .1 .2 .1 2.3 .4 .2 .2 1.8 1.6 100.0 |
64.2
1.3 9.3 .1 .4 .3 5.8 .8 3.2 .2 .3 2.2 .5 .1 1.4 .8 1.0 .1 .0* .7 .5 .1 .2 .1 2.3 .4 .2 .2 1.8 1.6 100.0 |
64.9
1.3 8.5 .1 .4 .3 5.9 .8 3.1 .2 .3 2.2 .5 .1 1.4 .9 1.0 .1 .0* .7 .5 .1 .2 .1 2.4 .4 .2 .2 1.8 1.6 100.0 |
* Rounds to zero but is not zero.
** May not add to 100.0 because of rounding.
Table 2
Estimated % of 1998 Population Assigned RUCAs By Various Assignment Rules
(see 5 above)
Rule 1-- 92.8%
Rule 2-- 0.6%
Rule 3-- 1.2%
Rule 4--.1%
Rule 5-- 3.2%
Rule 6-- 1.4%
Rule 7-- 0.7%
Total 100.0%
Table 3
RUCA Assignment Statistics
| A) % of population assigned per exact x.x RUCA code 93.0% | 93.0% |
| B) % of population assigned per x RUCA code (e.g., within group of 1s or 4s etc.) 93.4% | 93.4% |
| C) % of population assigned per hierarchy group of RUCA codes 97.7% (e.g., 1-3, 4-6, 7-9, &10) | 97.7% |
| D) % of population assigned per a basic RUCA rural-urban
categorization 98.1%
(urban = 1.0+1.1+2.0+2.1+2.2+3.0+4.1+5.1+7.1+8.1+10.1 large rural = 4.0+5.0+6.0 small rural = 7.0+7.2+7.3+7.4+8.0+8.2+8.3+8.4+9.0+9.1+9.2 remote small rural = 10.0+10.2+10.3+10.4+10.5) |
98.1% |
| E) % of population assigned per a basic RUCA rural-urban
categorization 98.7%
(urban = 1.0+1.1+2.0+2.1+2.2+3.0+4.1+5.1+7.1+8.1+10.1 large rural = 4.0+5.0+6.0 small rural = 7.0+7.2+7.3+7.4+8.0+8.2+8.3+8.4+9.0+9.1+9.2 +10.0+10.2+10.3+10.4+10.5) |
98.7% |
| F) % of population assigned per a basic RUCA rural-urban
categorization 99.1%
(urban = 1.0+1.1+2.0+2.1+2.2+3.0+4.1+5.1+7.1+8.1+10.1 rural = 4.0+5.0+6.0+7.0+7.2+7.3+7.4+8.0+8.2+8.3 +8.4+9.0+9.1+9.2+10.0+10.2+10.3+10.4+10.5) |
99.1% |
% of Population Assigned When 67% or Greater of a ZIP’s Population Fits Criteria (letters corespond with definitions above):
A) 92.6% (i.e., 92.6% of the population of ZIPs assigned to a code were the exact x.x code)
B) 93.2%
C) 97.9%
D) 99.3%
E) 98.9%
F) 99.2%
% of Population Assigned When 90% or Greater of a ZIP’s Population Fits Criteria:
A) 78.4%
B) 79.6%
C) 92.7%
vD) 93.7%E) 95.4%
F) 97.0%
% of Population Assigned When 100% of a ZIP’s Population Fits Criteria:
A) 62.8%
B) 64.2%
C) 85.1%
D) 87.2%
E) 90.0%
F) 93.5%
% of Population Assigned by Criteria For States (Highs and Lows) (note that 100%s are mostly rounded to 100%):
A) state highs (DC @ 100%, HA, UT, RI @ 98%, & MA, CA, NV @ 97%,) state lows (MS @ 78% , NC @ 81%, WV @ 85%, & AR, SC, IN @ 87%)
B) state highs (DC @ 100%, HA, UT, MA, RI @ 98, & 5 states @ 97%) state lows (MS @ 80% , NC @ 83%, WV @ 86%, AR @ 87%, & 4 states @ 88%))
C) state highs (DC @ 100%, UT, RI @ 100% rounded to 100%, & 12 states @ 99%) state lows (NC @ 93% & MS @ 94%, WI @ 95%, & 5states @ 96%)
D) state highs (DC @ 100%, & CO, RI, UT rounded to 100%) state lows (NC, MS @ 94%, & WI @ 95%)
E) state highs (DC @ 100%, & AZ, CO, DE, MT, NV, RI, SD, UT, WY rounded to 100%) state lows (NC @ 96%, & MS, OH, WI @ 97%)
F) state highs (DC @ 100%, & 18 rounded to 100%) state lows (NC @ 97%, & rest at 98 and 99)
% of Washington State’s Population Assigned Per Criteria of ZIP’s Population Fits Criteria:
A) 93.0%
B) 93.2%
C) 98.5%
D) 99.0%
E) 99.1%
F) 99.6%
Table 4
Correspondence of Assignment By RUCA Code
| RUCA Codes (v. 1.1) | Exact Assignment Match (x.x) % Est. 1998 Population |
Match Per Same Group* % Est. 1998 Population |
Match Per Same Rural/Urban Dichotomy**
% Est. 1998 Population |
| 1.0 (64.8)
1.1 (1.3) 2.0 (8.4) 2.1 (.1) 2.2 (.4) 3.0 (.3) 4.0 (6.9) 4.1 (1.0) 5.0 (2.2) 5.1 (.2) 6.0 (.3) 7.0 (2.7) 7.1 (.6) 7.2 (.1) 7.3 (1.8) 7.4 (1.0) 8.0 (.7) 8.1 (.1) 8.2 (.0) 8.3 (.5) 8.4 (.3) 9.0 (.1) 9.1 (.1) 9.2 (.1) 10.0 (2.2) 10.1 (.3) 10.2 (.2) 10.3 (.1) 10.4 (1.6) 10.5 (1.4)
|
94.5
79.9 32.3 21.2 24.1 18.8 86.9 91.0 23.1 14.6 15.8 79.9 48.6 54.4 66.6 60.1 23.9 10.2 10.3 22.4 18.9 22.5 15.7 13.9 50.4 26.0 17.3 23.4 26.9 32.2
|
98.8
96.4 85.3 86.1 68.5 43.7 95.1 75.9 85.1 78.0 73.3 92.7 53.0 58.8 80.4 74.7 87.1 48.8 62.8 76.8 70.8 78.4 70.1 55.9 59.4 (88.9)*** 33.6 (46.1)*** 24.6 (30.4)*** 32.2 (93.4)*** 47.7 (75.7)*** 40.9 (61.6)***
|
99.3
99.1 90.2 93.8 78.5 56.0 97.7 97.0 95.0 71.8 86.5 98.9 94.5 99.4 85.9 96.4 99.0 72.1 100.0 84.7 97.7 93.1 78.8 98.9 95.4 76.2 95.7 95.2 79.6 94.4
|
* Groups are 1s+2+3s, 4s+5s+6s, 7s+8s+9s, and 10s.
** Rural-Urban Groups
(urban = 1.0+1.1+2.0+2.1+2.2+3.0+4.1+5.1+7.1+8.1+10.1 rural = 4.0+5.0+6.0+7.0+7.2+7.3+7.4+8.0+8.2+8.3+8.4+9.0+9.1+9.2 +10.0+10.2+10.3+10.4+10.5)
*** Percentages in parentheses if 10s are grouped with 7s/8s/9s code group.
Note: The figures in Tables 3 and 4 are not easily interpreted. By virtue of their small numbers and transitional nature at the fringes of Urbanized Areas, the populations of some of the Census tract codes (e.g., 3.0s) are redistributed across many of the RUCA codes in the ZIP code approximation. Since there are nearly twice as many Census tracts as ZIP code areas, small Census tract transitional code areas that are not clustered are often subsumed by the code areas around them. Given that the ZIP areas are larger, this is appropriate. For example, RUCA code 3.0 Census tract population is distributed as follows across the ZIP code RUCAs from 1.0 through 10.5: 7.2, 0.0, 15.9, 0.2, 1.6, 18.8, 14.0, 6.9, 2.7, 0.1, 0.9, 1.6, 5.0, 0.2, 11.2, 2.0, 0.3, 0.0, 0.2, 2.2, 0.1, 0.0, 0.5, 0.0, 0.6, 0.3, 0.0, 0.0, 5.8, and 1.7 percent. Likewise, ZIP code RUCAs like 8.1 (a ZIP code area strongly tied to a small town but with a secondary work commuting flow of greater than 30%): 1) have a strong commuting relationship with a small town, 2) have a strong commuting relationship with an Urbanized Area, 3) are few in number, and 4) cannot have or be part of an Urban Place with a population in excess of 2500 population. Thus, the Census tract defined 8.1 populations are often assigned to urban codes or small rural codes. The RUCA code 8.1 Census tract population is distributed as follows across the ZIP code RUCAs from 1.0 through 10.5: 12.6, 0.0, 20.0, 0.0, 5.9, 1.5, 4.1, 4.3, 1.9, 0.0, 0.1, 1.4, 17.6, 0.0, 15.9, 0.0, 0.0, 10.2, 0.0, 2.9, 0.0, 0.3, 0.5, 0.0, 0.0, 0.0, 0.0, 0.0, 0.7, and 0.1 percent (the Urban category (see ** above) are underlined and those related to the small rural category are in bold type). Adding the urban and small rural category percentages together yields 93.1 percent. Other codes that are more numerous and more central to the settlement pattern such as RUCA code 4.0 are much less influenced by the Census tract to ZIP code translation. Nearly 87% of the Census tract RUCA 4.0 code population end up in the 4.0 ZIP code approximation areas. If the code area population percentages for the commuting related codes of 5s, 6.0, 7.2, 7.4, 8.2, 8.4, 9.2, 10.2, and 10.5 are added the sum is 97%.