Benjamin Bradshaw
Mar 14, 2018 · 5 min read

Here at Achievement, a division of Evidation Health, we are excited about using data actively contributed by Achievers to do research that leads to better health outcomes for everyone. Every day, we have the opportunity to use cutting-edge methods to answer questions that have either never been asked before, or previously researchers haven’t had the data to answer. In preparation for Air Quality Awareness Week, we decided to investigate whether air quality could be related to health outcomes and activity patterns within the Achievement population.


  • Air pollution is highly seasonal and different forms of pollution tend to peak at different times of the year.
  • Ozone is a type of pollution that has been linked to asthma and tends to peak in the months of June, July, and August in the northern hemisphere.

The chart below shows the EPA’s Air Quality Index (AQI) over a portion of 2017 for the county of Riverside, CA. In the plot below, you can distinguish the seasonal patterns.

  • The values above the dashed red line are considered “moderate” air quality. Moderate AQI is considered 51 to 100. The higher values indicate worse air quality.
  • Note: the two peaks with AQI > 300 may be sensor malfunctions.

Air Quality and Asthma: Is there a significant relationship?

We were interested in investigating whether there were general associations between user activity patterns (e.g. walking, sleep, heart) and the air quality in the region where Achievers lived. Since previous studies have found a link between ozone levels and asthma, we were also curious in exploring the relationship between air quality and user activity patterns.

Since ozone is typically highest in the summer months in the northern hemisphere (where the majority of Achievers currently live), we used data from June of 2017 to estimate a region’s typical annual peak ozone air quality from year to year. While this may change in the long term, it’s likely a safe estimate in the short term. Splitting our sample of Achievement users whose home region had an average daily AQI < 50 during this period (considered “good” by the EPA) and those whose average daily AQI >=50 (moderate or worse), we then compute prevalence rates between these two groups:

We find that the reported rate of asthma in “high AQI” regions is about 1% higher than in “low AQI” regions which is statistically significant.

A neat result! But there is a potential problem: people in “high AQI” regions tend to be people who live in cities. It’s possible that areas with higher AQI also tend to be areas where people commute more or eat worse, and those factors are the ones that are contributing to higher rates of asthma. Statisticians call this problem omitted variable bias, and it is a large consideration when conducting any sort of inferential analysis.

Searching for evidence of sleep disturbances in Achievement users with asthma

We have seen evidence that Achievement users in areas with higher AQIs (worse air quality) are more likely to have a reported diagnosis of asthma. As a next step, we were curious if we could replicate previous research in order to gauge whether asthmatic patients have increased sleep disturbances.

In order to do this analysis, we split our sample into those who have a self-reported diagnosis of asthma vs those who claim to not have an asthma diagnosis. Then, we look at differences in sleep patterns between the two groups.

One of the items we are able to infer using minute level data supplied by Fitbit is how many periods of “awakeness” a person experienced while in bed. In theory, we should see more periods of awakeness for users who report having asthma than those who don’t. In fact, that is exactly what we see in the figure below. At a population level, users with asthma generally have more periods spent awake during the night, and this lends evidence to the hypothesis that asthma patients have a more disturbed sleep.

Another item we might expect to see in the data is that on their “highest sleep” days, users who report having asthma spend more time in bed than others due to asthma attacks. Again, the data supports this anecdotal wisdom: when we look at days in the 95th percentile of days in terms of time spent in bed, we find that those in the asthma group spend significantly more time in bed.

Achievement is a diverse group of people and reflects the diversity of health and activity profiles of people all across the United States. This diversity allows us to conduct cutting-edge research with data that would otherwise be impossible to collect in such a short time period. So, props to you Achievers out there who are contributing to better health outcomes for everyone — faster! Not yet an Achiever? You can join us here.

Have you experienced any adverse reactions due to air quality or noticed disturbed sleep due to asthma? Let us know by commenting below!

Achievement - Support your health. Reward your life.

Benjamin Bradshaw

Written by

Data Scientist @evidationhealth

Achievement - Support your health. Reward your life.

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