Monday, March 9, 2015

Accuracy and Precision

Surfing for Accuracy (or Precision?)

A cousin of mine posted on Facebook that she was returning her Fitbit since it didn't seem to track her heart-rate properly. I had similar doubts about the step counting ability of my Garmin Vivofit. I've posted my observations, and was not sold about the measurements (especially when walking on a treadmill). 

Walking the Loop

My old house to our
Elementary School
Over the winter I walked the same basic loop, over and over again (increasing the sample size) and had very consistent step counts from the Garmin Vivofit that I bought from Amazon. I chalked up the minor variations to my stride -- on good days very aggressive (longer, therefore fewer) strides, and on bad days a shorter less energetic stride (but more of them).

According to the Vivofit

From my front door to the end of the sidewalk by the Montessori school was about 4000 steps - or two (2) miles. But it did vary, often by a few dozen steps up to 100 steps.

According to Elle (my BMW)

While driving home one evening I reset the odometer and measured from the driveway at the front of the Montessori school to my garage -- two (2) miles. Which didn't seem right - since the sidewalk and the middle of the street are slightly different lengths. But, I decided "good enough". 

Something Happened

Then I tried walking on a treadmill at the YMCA (where the speed/distance/step count didn't really jive) - and then I read my cousin's post, and then I had more doubts. 

Nothing in life is more pitiful that an INTP/J with doubts.  

I found Richard Byrne and his blog "Free Technology for Teachers" on Twitter (@rmbyrne) and added his blog to my Feedly (Twitter: @Feedly) content. He posted a neat measurement trick using Google maps. 

Bring up a Google Map with your starting location and right click. Then select Measure Distance. Click the path (works on streets, in the forest for trails, and even around or through bodies of water) staying as close to the curves as you like, and it will keep adding each additional point to the measurement. 

Distance from our old house to old elementary school -- 1.98 miles. 

The Bottom Line

Sure, somewhere out there is an athlete that is screaming at this post "your measurement resolution stinks" you could be off by 37.4 feet and never even know it!

The car (Elle) says two miles, the Vivofit says two miles, and Google maps says two miles. I'm going to let technology win this discussion and let my subconscious worry about the Participation Rate and the implications of negative interest rates in Europe

Thanks @rmbyrne!