Part 1: Preventing 7,000 deaths from heart disease alone among nonwhites each year

The press release from the University of Minnesota's web site reads:

A first-of-its-kind study by researchers at the University of Minnesota found that on average nationally, people of color are exposed to 38 percent higher levels of nitrogen dioxide (NO2) outdoor air pollution compared to white people.

The press release goes on to tell us:

...researchers estimate that if nonwhites breathed the lower NO2 levels experienced by whites, it would prevent 7,000 deaths from heart disease alone among nonwhites each year.

7,000 deaths - each year - prevented by breathing less NO2? That number seems....high...really high.

So I went and read their research paper.

An important issue is whether the NO2 disparities described above are relevant to public health. To investigate that question, we consider here one illustrative example: ischemic heart disease (IHD) annual deaths associated with NO2 concentration disparities between nonwhites and whites.

Here is what the author's write:

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.

Since there are numbers quoted and cited, I went looking for [39] to see what those numbers mean.

The "6.6% change in IHD mortality rate per 4.1 ppb NO2" comes from this paper. Table 4 shows the "Relative risks ...for the interquartile range of exposure in each pollutant (i.e., 5.3037 mg/m3 for PM2.5, 4.1167 ppb NO2, and 24.1782 ppb for O3). Values in parentheses are 95% confidence intervals."

Based on the results in this table, exposure to 4.1 ppb NO2 showed a 6.6% increase [(1.066 - 1) * 100] in risk for IHD. Another way to look at this result is:

• The risk of IHD in those exposed to 4.1 ppb of NO2 was 1.06 times as high as the risk of IHD compared to subjects who were exposed to less than 4.1 ppb NO2.

I am not going to question if, or if not, that number of 6.6% is valid. I am going to assume that it is.

Going back to the Clark et al paper, we are told that the annual death rate for IHD is "109 deaths per 100,000 people." Again...I am going to assume that this number is correct.

So we have these numbers. Assuming they are correct, how do they get us to preventing "7,000 deaths from heart disease alone among nonwhites each year?"

...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.

Oh...I see what they did...

From Wikipedia: The United States Census Bureau defines White people as those "having origins in any of the original peoples of Europe, the Middle East, or North Africa. It includes people who reported "White" or wrote in entries such as Irish, German, Italian, Lebanese, Near Easterner, Arab, or Polish." Whites constitute the majority of the U.S. population, with a total of about 245,532,000 or 77.7% of the population as of 2013.

So...with a total population of 323,730,000 in the US, 22.3% would be "nonwhites" for a total of 72 million. Since the authors don't cite where they got their "87 million people" from, I can only assume it was based on this type of thinking. [Note: I found it in the PDF attachment]

Let's use their number of 87 million (nonwhite) people.

If the incidence of IHD is 109 deaths per 100.000, then we would expect 94,830 of those 87 million to die from IHD each year.

If 4.1 ppb NO2 is associated with a 6.6% increase in risk and the risk of IHD is 109 per 100,000, we should see 109 x 1.066 = 116 per 100,000 or 7 more per 100,000 IHD deaths per year.

Based on my calculation, I get 6,258 more deaths. I think my estimate is correct based on this:

For example, say the absolute risk of a work injury is two per 100 workers. Due to an intervention, it drops to one injury per 100 workers. This yields a relative risk reduction of 50 per cent. Overall, in absolute terms, this means one less injured worker per 100.

All this number crunching is really not the issue here. What is bugging me is how the statement...:

 "it would prevent 7,000 deaths from heart disease alone among nonwhites each year."

...becomes the takeaway message from their research.

That number isn't even close to the reality at hand.

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