We are not the only ones curious about whether our activity level looks different when seen with different trackers. Bastian Greshake, co-founder of OpenSNP.org, has been comparing his FuelBand and his Fitbit for months. Here’s what he found.
Inspired by Ernesto’s post I wanted to take a look at how my data for the Fitbit and the FuelBand compare to each other. I started wearing the FuelBand in October of last year. Since then it has only left my wrist to recharge the battery. I was already carrying a Fitbit Ultra, which I’ve had since May 2012. I wear the FuelBand on my dominant arm. The Fitbit is usually clipped to the pocket of my jeans and I have it on my non-dominant arm while sleeping. From my day-to-day experience I have a sense that FuelBand steps are usually a good way below the Fitbit steps. But I also thought that the difference was getting smaller, probably due to firmware updates on the FuelBand.
Using the Fitbit-API (and it’s integration into openSNP) it’s quite easy to get a file that contains all step counts measured with the Ultra. If you have an openSNP account you can download the complete file, also including sleep data and body measurements here. Unfortunately the Nike+ API isn’t ready yet, so one needs to manually scrape the data. As this is boring work that can’t easily be automated I only got FuelBand step data back to 2013/11/16. Still, that should be enough to get a first insight on how both devices compare.
The simplest way to compare both devices in terms of step count is to calculate the difference (steps counted by Fitbit) – (steps counted by FuelBand) for each day. Positive values show more steps counted on the Fitbit, negative values show more steps counted on the FuelBand. One problem in comparing arises if you frequently travel through time zones: While you can easily adjust the timezone using the FuelBand iOS application there’s no easy way to change the time zone on the Fitbit if you’re traveling. Thus I excluded all days where the Fitbit & FuelBand timezones don’t match up. After removing those data and calculating the differences this is what came up while graphing my data:
For most of the days my initial feeling that the Fitbit tends to report larger step counts holds true, although there are also some cases where the FuelBand reported much higher step counts than the Fitbit. The largest difference goes up to 3126 more steps counted on the Fitbit, the smallest difference is 21 more steps counted on the FuelBand, so there is tremendous variation in how much the devices disagree. My feeling that the difference is getting smaller due to firmware updates on the end of the FuelBand seems to be untrue. (I couldn’t find any data on when the firmware updates where released. If you should happen to know them please let us know and we can investigate this further.)
Looking at the pattern above I came to the idea that the measured difference between the FuelBand and the Fitbit might be explained by how active I was on a given day. So I plotted the step counts for the Fitbit along in the same graph (divided by 10 to make the scale of the Y-axis look a bit nicer):
While there are some outliers (especially to the beginning) it seems to me that activity is indeed one of the factors that influence on how close the step counts of the Fitbit and FuelBand will match. Days where the Fitbit measures lots of steps tend to be those where the FuelBand underestimates the step count in relation to the Fitbit. On days where the step count on the Fitbit is low the FuelBand often overestimates the step count in relation to the Fitbit. To check this, I looked at a similar graph using Fuelband steps as my activity measure: the pattern is the same.
My guess is that these differences arise from both the algorithms used to calculate steps and the difference in where the devices are worn. On days that I walk less, the FuelBand may inflate the step count due to wrist movements. On days that I walk a lot, the FuelBand count could be falsely low because I’m wearing it on the wrist and steps may not be detected. Also, the FuelBand seems to differentiate between steps and other movements, so it may be that the FuelBand sees the activity but does sometimes mistakes it for something other than steps.
You are invited to play along.
Basic step data is here: fitbit vs fuelband.
If you want stairs climbed, sleep, etc., in csv format, look here: more Fitbit data.
Thanks very much Bastian. We invite anybody to share what they learn from their own experiments.