Fun post & interesting analysis... Makes me wonder how different the results would be for a sample of people who don't link their device to their Twitter account. I suspect the number of steps in the first quartile would be considerably lower... (not sure how you would collect the data though?!?)

Similar to your questions relating to the size of a step, there are so many other questions relating to fitness level, heart-rate, time of the day of activity, time series analysis etc etc

Indeed statistical voyeurism! :-)

Cheers,
Michelle