<p>WHO page <a href="https://www.who.int/data/gho/data/indicators/indicator-details/GHO/ambient-and-household-air-pollution-attributable-death-rate-(per-100-000-population)" rel="nofollow noreferrer">Indicator 3.9.1: Mortality rate attributed to household and ambient air pollution (per 100 000 population)</a> has this information in the &quot;metadata&quot; tab:</p>
<blockquote>
<p><strong>Method of estimation:</strong></p>
<p>[...]
To estimate the combined effects of risk factors, a joint population attributable fraction is calculated, as described in Ezzati et al (2003).</p>
</blockquote>
<p><a href="https://doi.org/10.1016/S0140-6736(03)13968-2" rel="nofollow noreferrer">Ezzati et al (2003)</a> defined the joint <a href="https://www.who.int/data/gho/indicator-metadata-registry/imr-details/1287" rel="nofollow noreferrer">population attributable fraction</a> (<span class="math-container">$PAF$</span>) for <span class="math-container">$n$</span> biologically independent and uncorrelated risk factors, as (their equation 2):</p>
<p><span class="math-container">$PAF = 1 - \prod_{i=1}^n(1-PAF_i)$</span></p>
<p>where <span class="math-container">$PAF_i$</span> is the population attributable fraction of individual risk factors.</p>

CC BY-SA 4.0
2022-03-24T15:00:09.157Z
+1. Nice find. Is there enough information to show the calculation? i.e. how to get to 7 million total from the 4.2 and 3.8 million figures? The Ezzati paper is behind a paywall, and WHO's explanation only includes the formula, not the calculation.
LShaver
CC BY-SA 4.0
2022-03-25T10:07:03.453Z
I've had a look but the data seems to be only by country, I couldn't find global data. So I guess to try to reproduce the calculation, you'd have to calculate each country's contribution to the total by multiplying its mortality rate by its population...
Jean-Marie Prival
CC BY-SA 4.0
2022-03-24T13:58:07.650Z
2022-03-24T13:58:07.650Z
Jean-Marie Prival
<p>The WHO's <a href="https://www.who.int/health-topics/air-pollution" rel="nofollow noreferrer">landing page on air pollution</a> includes three different estimates of deaths due to air pollution:</p>
<ul>
<li>7 million total</li>
<li>4.2 million due to outdoor (ambient) air pollution</li>
<li>3.8 due to household (indoor) air pollution</li>
</ul>
<p>Obviously, <code>7 &lt; 4.2 + 3.8</code>, so there must be some way in which they decide some of those deaths were caused by a combination of indoor and outdoor air pollution. <strong>But what is this methodology?</strong></p>
<hr />
<p>It's unclear where that 7 million figure originates from, so there's a chance it's a case of <a href="https://xkcd.com/978/" rel="nofollow noreferrer">citogenesis</a>, and someone just did the math wrong. It appears in WHO's 2021 <a href="https://www.who.int/publications/i/item/9789240034228" rel="nofollow noreferrer">global air quality guidelines</a> (section 1.3.3), which cites <a href="https://www.who.int/airpollution/data/AAP_BoD_results_May2018_final.pdf?ua=1" rel="nofollow noreferrer">Burden of disease from ambient air pollution for 2016</a>, where the 7 million figure <em>does not</em> appear.</p>

<air-pollution>
How does the WHO calculate the interaction of mortality effects from indoor and outdoor air pollution?
LShaver
# How does the WHO calculate the interaction of mortality effects from indoor and outdoor air pollution?

(Asked by: username_0 on 2022-03-22)

The WHO's [landing page on air pollution](https://www.who.int/health-topics/air-pollution) includes three different estimates of deaths due to air pollution:

* 7 million total
* 4.2 million due to outdoor (ambient) air pollution
* 3.8 due to household (indoor) air pollution

Obviously, `7 < 4.2 + 3.8`, so there must be some way in which they decide some of those deaths were caused by a combination of indoor and outdoor air pollution. **But what is this methodology?**

---

It's unclear where that 7 million figure originates from, so there's a chance it's a case of [citogenesis](https://xkcd.com/978/), and someone just did the math wrong. It appears in WHO's 2021 [global air quality guidelines](https://www.who.int/publications/i/item/9789240034228) (section 1.3.3), which cites [Burden of disease from ambient air pollution for 2016](https://www.who.int/airpollution/data/AAP_BoD_results_May2018_final.pdf?ua=1), where the 7 million figure *does not* appear.

**Tags:** air-pollution


---

## 1 answers

### Answer by username_1 on 2022-03-24. Score: 2

WHO page [Indicator 3.9.1: Mortality rate attributed to household and ambient air pollution (per 100 000 population)](https://www.who.int/data/gho/data/indicators/indicator-details/GHO/ambient-and-household-air-pollution-attributable-death-rate-(per-100-000-population)) has this information in the "metadata" tab:

> **Method of estimation:**
>
> [...]
> To estimate the combined effects of risk factors, a joint population attributable fraction is calculated, as described in Ezzati et al (2003).

[Ezzati et al (2003)](https://doi.org/10.1016/S0140-6736(03)13968-2) defined the joint [population attributable fraction](https://www.who.int/data/gho/indicator-metadata-registry/imr-details/1287) ($PAF$) for $n$ biologically independent and uncorrelated risk factors, as (their equation 2):

$PAF = 1 - \prod\_{i=1}^n(1-PAF\_i)$

where $PAF\_i$ is the population attributable fraction of individual risk factors.

> **Comments:**
> **username_0**: +1. Nice find. Is there enough information to show the calculation? i.e. how to get to 7 million total from the 4.2 and 3.8 million figures? The Ezzati paper is behind a paywall, and WHO's explanation only includes the formula, not the calculation.  
> **username_1**: I've had a look but the data seems to be only by country, I couldn't find global data. So I guess to try to reproduce the calculation, you'd have to calculate each country's contribution to the total by multiplying its mortality rate by its population...  

---

