As more schools begin using Moki, we’re now able to measure physical activity levels across large numbers of primary school children. But for these data to be meaningful, it’s essential to understand whether differences between children are genuine, rather than the result of variation in device performance.
To investigate this, Georgina Wort — a doctoral researcher at the University of Bath — carried out comprehensive testing to examine the reproducibility of Moki devices under standardised conditions. For the study, she used a multi-axis simulation table (often called a Shaker Table) to precisely replicate movement.
How the testing worked
The Shaker Table moves in a highly controlled way over a specific distance and at specific speeds. Georgina attached more than 100 Moki accelerometers (the internal sensor within each band) to the table and ran two-hour tests at both lower and higher speeds (2.5 Hz and 3.5 Hz).
Because every accelerometer experienced exactly the same movement at each speed, they should, in theory, produce the same activity count. Any variation between the readings would therefore reflect technical variation between devices rather than true differences in movement.
Across the full programme, the bands recorded around five million steps.
What was measured
Georgina assessed variation using the Coefficient of Variation (CV) — a standard way of evaluating consistency in scientific measurements. She 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 differences between children, or changes within 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 tests such as cholesterol, this might be as low as 3%.”
The results
The testing found that Moki devices had a CV of:
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0.1% at the lower speed
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0.8% at the higher speed
“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.”
Why this matters
This is an outstanding result for us at Moki. It means we can be genuinely confident in the day-to-day performance of the bands children wear in schools. It also gives researchers like Georgina reliable data they can trust when studying physical activity in primary school children.
Ultimately, the more accurate the device, the clearer the insights — and these results show that Moki provides an exceptionally strong foundation for understanding movement in schools.