How Low Can We Go? Problems with ZIP Code Level Analyses

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How Low Can We Go? Problems with ZIP Code Level
Analyses

• Lance Miller, MA
• Andrea Rodriguez, MS
• San Bernardino County Department of Public Health

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Presentation Overview

• Problem statement
• Purpose
• San Bernardino County examples
• Muscoy
• ZIP code 92401
• Conclusions
• Solutions

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Problem Statement

• Public health departments use ZIP code level
  analysis to identify areas where program
  resources are needed most
• Flawed source data can lead to erroneous
  conclusions and inaccurately targeted public
  health interventions

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Purpose

• Present two problems the San Bernardino County
  Public Health Department has encountered with ZIP
  code level analysis
• Discuss possible solutions to these problems,
  likely faced by state and local health agencies
  nationwide

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The Muscoy Problem
Where the heck is Muscoy?
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Muscoy, California
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About Muscoy

• Unincorporated area
• Population in 2000 9,000 residents
• Land area 2.9 sq. miles
• Demographics
• Educational attainment
• Unemployment
• Income and poverty

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Why Muscoy?

• Lack of infrastructure
• Increase in violent crime
• Restless residents

• Call for community needs assessment

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Muscoy Needs Assessment

• Resident survey
• Census data
• Birth outcomes
• Cause of death data

10 births
7 deaths
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Muscoy is within 92407
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What else is in 92407?

• Actual city name is San Bernardino
• Acceptable city names include Arrowhead Farms,
  Devore Heights, Muscoy, and Verdemont
• Are people using San Bernardino, 92407 when
  they truly reside in the area of Muscoy?
• How will I investigate this???

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Geocoding!

• Using GIS software to convert street addresses
  into latitude and longitude coordinates
• Makes locating addresses and viewing multiple
  locations on a map instantly possible

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Geocoding

• Geocoding is a must if we want to examine births
  and deaths in Muscoy
• Teen birth events
• Smaller data set more manageable
• Data exploration

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Startling Results

• ZIP code results Less than 5 births to teen
  female residents of Muscoy
• Geocoded results 40 births to teen female
  residents of Muscoy
• Thats well over 8 times as many births!!!

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Is this an isolated incident?

• NO!
• During presentation preparation, we discovered
  something similar happened before
• Routine vital stats report for county health
  officer led to investigation of extremely high
  teen birth rate in ZIP code 92401

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How the 92401 Study Began
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Routine Report Finding
Note Teen birth rate defined as number of live
births to mothers aged 15-19 years per 1,000
female population aged 15-19 years. Sources 1.
California Department of Health Services, Birth
Files. 2. U.S. Census Bureau, 2000 Census,
Summary File 1, Table P14. Prepared by San
Bernardino County Department of Public Health.
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Health Officers Question

• Is 92401 high teen birth rate
• artifact of data, or
• real phenomenon?
• To answer
• Geocoded all births indicating 92401 residence
• What zip code was each birth really in (according
  to mapped street address)?

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Where is ZIP code 92401?
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Where is ZIP code 92401?
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Mapped teen births reported as 92401
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Findings

• Of 43 birth certificates indicating 92401

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Findings
Note Teen birth rate defined as number of live
births to mothers aged 15-19 years per 1,000
female population aged 15-19 years. Sources 1.
California Department of Health Services, Birth
Files. 2. U.S. Census Bureau, 2000 Census,
Summary File 1, Table P14. Prepared by San
Bernardino County Department of Public Health.
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Health Officers Conclusions

• Perhaps zip codes are too small to do detailed
  analyses
• We have used zip code data which may have
  been misleading to some degree if the data at
  this level is really so unreliable
• Given all these analysis problems, should we
  expend program resources targeted to this area?

Source Thomas Prendergast, MD, MPH, personal
correspondence with Evelyn Trevino, April 2003.
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Conclusions

• Cannot rely on ZIP codes alone for accurate
  geographic analysis
• Data entry error
• The nature of places
• In order to make valid conclusions, residence
  street addresses must be geocoded

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Solutions

• Good START GEOCODING!
• Better Birth and death events geocoded at the
  state level
• Best Address validated and assigned coordinates
  at point of entry
• Essential to all Understanding the importance of
  accurate data collection

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Our Contact Information

• Lance Miller, Statistical Analyst
• [phone]
• lmiller_at_dph.sbcounty.gov
• Andrea Rodriguez, Statistical Analyst
• [phone]
• arodriguez_at_dph.sbcounty.gov