Saturday, May 21, 2016

Part 2: Preventing 7,000 deaths from heart disease alone among nonwhites each year

The amount of peer reviewed research papers that contain exaggerated claims of association and statistical - but meaningless - results that I come across is disheartening.

I don't want to be skeptical of every peer reviewed research paper I read, but I am.

The authors of this paper "National Patterns in Environmental Injustice and Inequality: Outdoor NO2 Air Pollution in the United States," are professors in the Civil engineering department at the University of Minnesota.

Their press release for their paper is titled:
Groundbreaking nationwide study finds that people of color live in neighborhoods with more air pollution than whites  Gap results in an estimated 7,000 deaths each year among people of color from heart disease alone
That claim of 7,000 deaths is front and center.

When I read the press release I was skeptical of that claim. I go where the numbers take me. I am just having a difficult time with their findings:
Assuming a 6.6% change in IHD mortality rate per 4.1 ppb NO2 [39] and US-average IHD annual mortality rates (109 deaths per 100,000 people [40]), reducing NO2 concentrations to levels experienced by whites (a 4.6 ppb [38%] reduction) for all nonwhites (87 million people) would be associated with a decrease of ∼7,000 IHD deaths per year.
I got hung up on the "87 million people." Where did that number come from? I don't mean where did they get it from, I mean why did they use it?

Once that brain nugget planted in my thinking as I read, I started trying to figure out what they were going after. I can only speculate as to their motives. What I write about are my questions and research into the validity of their claim.

The best place to start, me thinks, is with this table tucked away in their supporting data.

Looks like they used 2000 census data for the nonwhite population. What I cannot figure out is how they calculated the 14.5 ppb NO2 concentration for nonwhites. That number is critical in their claim of 7000 additional deaths from IHD.

According to their paper, that concentration is "population weighted."

If I understand this correctly, each "Block Group" or "BG" - defined as "the smallest Census geography with demographic data (race-ethnicity, household income, poverty status, education status, and age) reported in the 2000 Census" with a mean BG sizes of "1.1 km2 (urban), 185 km2 (rural),
and 45 km2 (mixed)" and a  mean (standard deviation) BG population of "1,350 (890) people."

The "population-weighted NO2 concentration" was calculated by summing up the concentration of NO2 in the BG multiplied by the population of the group. This sum was then divided by the sum of all of that group's population. I cannot offer an opinion on this method's validity or accuracy. I can, however, ask a couple of questions.

First, based on the data in the Excel spreadsheet they link to, this is what I calculated for the data identified as "urban":

Those averages are calculated from 448 urban areas within the US containing 119,643 BGs and a population of  160.8 million folks.

Call me skeptical, but if you are going to tell me the mean NO2 concentration for whites is 9.9 ppb - which is close to the mean concentration for 448 urban areas - then how do you support nonwhites in these 448 urban areas living in an average concentration of 14,5 ppb?

This means that within an urban area, whites live within the mean concentration of NO2 and nonwhites live in areas two standard deviations outside of this - as an average??

Call me intrigued.

What looks strange to me is this; if the population-weighted concentration is calculated and used, then wouldn't we see a very large difference in the concentration of NO2 for low-income nonwhites when compared to high-income whites?

If environmental justice is in play, pollution is more prevalent in low-income areas. High-income areas would be further away from highways and would have less NO2 spewing industries in their backyards.

If my logic is correct, low-income nonwhites would be exposed to more NO2 than high-income whites. Wouldn't we see a difference in the population-weighted NO2 concentration greater than 4.6 ppb (the difference between the population-weighted mean NO2 concentration for whites and nonwhites)?

Call me confused, but the data in their Excel sheet shows an average Low-Income Nonwhite (LIN) Population-weighted Concentration  of 11.1 ppb for 448 urban areas and an average High-Income White (HIW) Population-weighted Concentration of 9.8 ppb.

Call me perplexed, but that's a difference of 1.3 ppb for these two VERY different groups.

Are we sure about that number of 14.5 ppb NO2 represents the exposure concentration for nonwhites?

And are we sure that 87.000.000 people - the total nonwhite population in the US in the year 2000 - lives in this concentration of 14.5 ppb while all whites live in areas with 9.9 ppb?

Call me skeptical, but that's what I see is the problem with their conclusion. They claim:
Gap results in an estimated 7,000 deaths each year among people of color from heart disease alone.
That's based on an NO2 concentration of 14.5 ppb for 87,000,000 people - which is the total population of nonwhites in the US.

Next post: Part 3: Preventing 7,000 deaths from heart disease alone among nonwhites each year

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