The Shaker Test - How reliable is the data from a Moki Band?
As more and more schools start to use Moki, we are able to measure the physical activity levels in large numbers of primary school children. But for the data we gather to be valuable, it is really important to establish whether any observed differences between children are genuine and not caused by variation in the performance of the devices.
Georgina Wort, a doctoral researcher from the University of Bath, carried out comprehensive testing to examine the reproducibility of Moki devices under standardised conditions. To do this, she used a unique multi-axis simulation table (otherwise known as a Shaker Table).
The Shaker Table moves in a very precise way over a specific distance and at specific speeds. Georgina strapped over 100 Moki accelerometers (the part inside the band) on to the Shaker Table and tested them for two hours over lower and higher speeds (2.5 Hz and 3.5 Hz). This meant all the accelerometers experienced exactly the same movement at each speed and should have recorded the same level of activity. Any variation between readings is caused by technical variation due to differences in performance between accelerometers.
Collectively, across both speeds, the bands recorded approximately 5 million steps during the test programme.
Georgina explains: “All measurements will have some variation, but we want this to be as small as possible so that we can reliably pick up and measure both differences between children; or differences in the same individual before and after an intervention. Variation can be assessed using Coefficient of Variation (CV). Common clinical blood tests have a CV less than 12%, although for some common tests such as cholesterol, this might be as low as 3%.”
The results from Georgina’s testing found that the CV for Moki was just 0.1% at the lower speed and 0.8% at the higher speed (See Graph Below).
“These results are extremely encouraging,” Georgina says. “They show that the Moki accelerometers have a very high level of reproducibility with a CV less than 1% when tested under carefully controlled laboratory conditions. This means that if a group of Moki accelerometers experience exactly the same movement, they will give readings which are very close to each other.”
This is a great result for us here at Moki, as it means we can have real confidence in the performance of the bands children are wearing every day. It also helps researchers like Georgina understand more about physical activity levels in primary school children, by providing them with solid data they know they can trust.