Step by Step

The distribution of daily step counts

In addition to the daily average resting heart rate, we can obtain the daily step count from connected wearable fitness devices. Together with the resting heart rate, the step count is an important parameter for this study. As you can read in our post, The Pulse of the Nation, deviations from the average resting heart rate could indicate fever. However, resting heart rate may also deviate for various unrelated reasons.

By taking the step count into consideration as well as the resting heart rate, we can obtain a stronger indicator for fever: If your daily step count is much lower than your average step count, while your resting heart rate is significantly higher than baseline, it is more likely that fever is the underlying culprit. Thus, we obtain stronger results when combining step count and heart rate in our analysis.

However, before combining both parameters into one analysis, the step count itself needs to be analyzed on its own. By doing this, important variations due to weekday patterns or weather factors can be identified first. Moreover, step counts may even vary regionally between rural and urban areas. Taking all this into consideration, we aim to establish a solid reference baseline for further analyses.

Step count statistics for Germany and the federal states

To determine the typical daily step count and variation of donors in Germany, we plotted the the distribution of average daily step counts for all of Germany and each of the federal states:

Daily step count in Germany and the federal states. The step count of all donors from April 4, 2020 and May 18, 2020, is shown above. Indvidual states can be selected via the lower menu panel. We can see that the number of steps does not appear to differ significantly between federal states. Rather, it follows a national trend.

As can be seen in the figure above, typical daily values fall between 5,000 and 7,000 steps, with a fairly broad variation. Some donors even show a significantly higher step count. Variations between different German states, on the other side, are rather insignificant, leading to a uniformly shaped step count curve.

The step count map

Similar to the Resting Heart Rate Map, we can determine the average step count per district in Germany. The result is shown in the following map.

Daily average step count map. We calculated the average daily step count for each German district and found regional variation between 6,500 (light green) and 8,500 (dark green) steps per day. Typically, donors in rural areas take more steps per day on average than donors in urban areas.

The map depicts the average daily step count, computed for each district during the period from April 12 to May 18, 2020. The variation around the mean extends between 6,500 and 8,500 steps a day. In some regions, e.g. in Thuringia’s Kyffhäuserkreis and Schmalkalden-Meinigen, the step count is significantly elevated compared to the nation-wide average daily step count. Also, there is a clear difference between urban and rural areas in general. Donors in urban areas tend to take less steps a day than donors in rural areas.

Temporal stability of the step count parameter

Now, let’s look at the temporal stability of the step count. The below figure depicts the average step count for all of Germany as a function of time between April 12 and May 18, 2020.

Nation-wide average step count as a function of time. The green line represents the average daily step count within a time frame of a couple of weeks. It is situated between 6,000 and 7,000 steps per day. The shaded region marks the confidence interval of daily step counts, i.e. the region in which all individual step counts fall. Weekends are indicated by the grey shaded regions.

We can see that the daily step count follows roughly a constant curve. However, long-term tends cannot be predicted. The daily average is between 6,000 and 7,000 steps. Compared to the average daily resting heart rate, the step count displays higher variation (see Figure 2 in this post)). Moreover, weekends, especially Saturdays, are more prone to higher step counts than other weekdays.

Average daily step count in German states

Now the question arises whether the number of steps of the donors differs regionally. The figure below shows the average daily step count of donors for each of the German states.

Average step count in German states. The average step count for each German states is represented by a colored line. Individual states can be selected in the menu panel. It can be seen that weekends, marked by the grey shaded regions, show an increased step count, particularly on Saturdays.

In this figure, we can see that donors walk or run more frequently in some states as compared to others. In Hamburg and Bremen, for instance, the average step count is typically lower, whereas donors in Thuringia and Saxony are more “on-the-go” than donors in other states.

In addition, this figure clearly shows that the average number of steps on weekends, specifically on Saturdays, is higher than on weekdays.

Variability of step counts

The average number of steps per day, whether nation-wide or district-wide, is an important measure for this study. However, it is not the only statistically relevant value. We are also interested in the variability in the number of steps, which is the magnitude of the distribution. The variation can be determined via another statistical parameter, the standard deviation, which determines how far individual values ​​are from the mean.

The following figure depicts the standard deviation of the step count as a function of time for each federal state.

Variability of daily step counts. Standard deviation in the number of steps for each federal state as a function of time for the period from April 12 until May 18, 2020. States are indicated by individual curves, which can be selcted via the menu panel. Weekends are depicted by the grey shaded regions.

This figure shows that, the variability in the number of steps increases significantly on weekends and public holidays compared to weekdays. This is seen across all federal states.

Another important statistical parameter that requires attention is the coefficient of variation, which describes the relation between standard deviation and statistical mean. It is sometimes referred to as the “relative standard deviation”. The figure below depicts the coefficient of variation as a function of time for Germany.

Coefficient of variation of the daily number of steps. The curve shows the coefficient as a function of time nationwide. The coefficient shows very clear peaks on Saturdays. Weekends are marked in gray.

What next?

The following analyses include combining the resting heart rate and the step count in order to identify statistical and dynamic effects. In the end, both parameters will comprise the basis of a fever-detection algorithm, which will be applied at the district level in order to detect sudden spikes of fever-like symptoms.

Annika Rose
Annika Rose
PhD Student
Dirk Brockmann
Dirk Brockmann

Head of Research on Complex Systems Group