Asthma-related Hospital Admissions
vs Ozone Concentrations
in Texas
Draft deliberative document – do not quote or cite
Chief Engineer’s
Office • The Mont Belvieu Puzzle; •JJ& RN John
• AprilJolly
8, 2010 • Page
1 xx, 2010
CEO/AQD
• May
Research Questions
1. In ten of Texas’ most populated counties, how well do ozone
concentrations and hospital admissions (due to asthma)
correlate?
2. How are hospital admission rates and ozone concentrations
changing over time in each of these counties?
3. Using all 31 counties with regulatory ozone monitors, do
counties with higher summertime ozone concentrations have
higher summertime hospital admissions due to asthma?
Chief Engineer’s Office • The Mont Belvieu Puzzle; JJ& RN • April 8, 2010 • Page 2
Methods
• Hospital admissions
– Obtained age-adjusted asthma-related hospital admissions (AA rate)
data by quarter and county, 2005-08, from Texas Health Care
Information Collection (THCIC), Center for Health Statistics, Texas
Dept of State Health Services (DSHS)
• Ozone
– Obtained daily peak 8-hr ozone measurements, from TCEQ MOTHER
database, for all 82 regulatory monitors in Texas from 2005-08
– Calculated, for each quarter/year at each of these monitors, average
peak 8-hr ozone
– Averaged these values by county for the 31 counties with regulatory
monitors *
* The 32nd county with a regulatory monitor, Brewster County, was excluded from analysis.
Uncertainties
• Hospital admissions data are by quarter and county
– No finer temporal/spatial resolution available
– Therefore cannot determine if hospitals nearer to higher ozone levels
see more asthma admissions
• Ozone concentration data
– By averaging across a county, we lose spatial resolution – unable to
determine ozone gradients within the county
– By averaging data by quarter, we lose temporal resolution – there may
be episodes of crucial importance to health that are masked by the other
days in the quarter
Analyses
1. Time Series Graphs of Ozone vs Hospital
Admissions
2. Least Squares Linear Regression –
Average Ozone vs AA Rate
for 10 heavily-populated and/or highly industrialized
Texas counties
Bexar County
Cameron County
Collin County
Dallas County
Denton County
El Paso County
Harris County
Jefferson County
Tarrant County
Travis County
Summary (analyses 1 and 2)
• Asthma-related admissions rate (AA rate) inversely
correlated with average ozone in 9 of the 10 counties
– 8 counties show highest AA rate in Q4 and Q1, for most or all years, with
highest ozone almost always in Q2/Q3
• Travis county had highest AA rate Q2, Q3, Q4
– Of the 9 counties, 6 have inverse correlations that are statistically significant
at .05 level
– Cameron county is an outlier: its AA rate and average ozone are positively
correlated (see bullet on next slide) due to unusual ozone seasonal patterns
• Changes seen in average ozone across time period
– 8 of 10 counties showed decreases in Q3 ozone in 07-08 vs 05-06
– 3 of 10 counties appear to show overall decreases in AA rate, but this has not
been quantified
Summary (analyses 1 and 2)
• Cameron County has very different ozone seasonality than
the other counties
– Its lowest average quarterly ozone is consistently in Q3 (July –
September) – markedly lower than other quarters
• Harris County surprises
– According to the ozone metric used here (average daily peak 8-hr ozone,
by quarter), Harris shows lower ozone than might be expected (ranks 19
of 31 monitored counties)
– By this metric, Q2 ozone is markedly higher than Q3 in most years, even
though this county typically shows largest number of exceedance days in
August/September
– Less seasonal difference in AA rate (along with Travis County) than the
other 8 counties
Analyses
3. Relationship of 3rd-Quarter Mean Peak
Daily Ozone and 3rd-Quarter Asthma-related
Hospital Admissions
All 31 Counties Combined
Kleberg and McLennan counties have 2 quarters apiece of 3rd-quarter data. The other 29 counties
represented here have 4 years of 3rd-quarter data.
Summary (analysis 3)
• What is relationship between ozone and AA rate during
peak ozone season, when all 31 counties combined?
– 3rd quarter (July – September) is expected to be peak ozone season
• Answer: When all counties are combined, essentially no statistical
relationship between average 3rd quarter ozone and 3rd quarter AA
rate
• The lack of relationship suggests that something other
than ambient ozone is driving summertime hospital
admissions
Analyses
4. Relationship of Quarterly Mean Peak
Daily Ozone and Quarterly Asthma-related
Hospital Admissions
All 31 Counties Analyzed Separately
Statistics on Mean Quarterly Peak Daily Ozone vs Quarterly AA
Rate, 2005-08, for 31 Texas Counties with Regulatory Air
Monitors
County
Collin
Dallas
Denton
Gregg
Travis
Harris
ElPaso
Hunt
Parker
Rockwall
Hood
Tarrant
Cameron
Bexar
Harrison
Hays
Johnson
Victoria
Kaufman
Smith
Brazoria
Montgomery
Nueces
Ellis
Kleberg
Orange
Jefferson
McLennan
Webb
Galveston
Hidalgo
slope
-0.058
-0.059
-0.072
-0.086
-0.057
-0.059
-0.072
-0.093
-0.052
-0.038
-0.065
-0.031
0.089
-0.074
-0.040
0.085
-0.051
0.213
-0.052
-0.028
-0.027
-0.021
0.070
-0.028
0.046
0.040
-0.027
-0.024
-0.020
-0.015
-0.009
R_square
0.63
0.57
0.51
0.49
0.45
0.43
0.35
0.24
0.19
0.17
0.16
0.16
0.16
0.14
0.14
0.13
0.11
0.10
0.09
0.08
0.06
0.04
0.04
0.03
0.02
0.02
0.02
0.01
0.01
0.00
0.00
p_value
0.000
0.001
0.002
0.002
0.004
0.006
0.016
0.052
0.093
0.111
0.122
0.123
0.131
0.155
0.159
0.259
0.211
0.242
0.273
0.283
0.369
0.458
0.464
0.545
0.819
0.607
0.633
0.865
0.783
0.828
0.885
Significant at .05 level
These are sorted by
Y
descending R
Y
Y
square.
Y
(Statistics for counties in
Y
yellow were also seen in
Y
slides 7-25.)
Y
Note that these 31
counties roughly break
down into 3 groups:
1. Strongly inversely
correlated (first 7
counties) – all are
significant at .05 level
2. Weakly correlated (Rsquare .10 to .24) – no
correlations are
statistically significant
– of these 11 counties, 3
are positively
correlated
3. Essentially
uncorrelated (R-square
< .10) – 13 monitors
with AA rate essentially
unrelated to average
peak ozone.
Summary (overall)
• Based on quarterly average data, evidence presented
here suggests that asthma-related hospital
admissions are either inversely correlated, or
uncorrelated, with ozone levels
– Counties with higher ozone levels show stronger
anticorrelation between ozone levels and AA rate
– Counties with lower ozone levels show little correlation
between AA rate and ozone
• This suggests ambient ozone concentrations are not
the primary cause of asthma-related hospital
admissions
Possible Future Analyses
1. Alter the metric used to represent high ozone
–
Currently the “Mean Peak 8-hr Ozone” favors monitors with consistently
elevated peak ozone but few/none very high days (e.g. DFW) rather than
monitors with some low/modest days and a minority of very high days (e.g.
HGB)
–
This results in Harris county having lower mean ozone than the 4 principal DFW
counties
–
Could do geometric mean – better covers data that are skewed, e.g. Houston
–
Would an area with low/modest ozone, and a minority of very high days be
expected to show more asthma-related health effects than an area with +/consistently elevated, but rarely high, ozone concentrations?
2. Look at 1999 – 2004 data
–
Summertime ozone levels higher in those years than later years
–
Those data are not presently ready to analyze, but could be made so if needed