Research: Movement Devices are not created Equal

Sandroff BM, Motl RW. Comparison of ActiGraph activity monitors in persons with multiple sclerosis and controls. Disabil Rehabil. 2013;35(9):725-31.

Purpose: The current study compared output from the vertical axis of two
models of ActiGraph accelerometers under free-living and laboratory
conditions in persons with multiple sclerosis
(MS) and matched controls. 

Method: The sample included 41 cases of MS
and 41 controls matched by age, sex, height and weight. Participants
concurrently wore 7164 and GT3X accelerometers for 6 days under
free-living conditions, and undertook up to five, 6-minute periods of
walking at five speeds on a motor-driven treadmill. 

Results: Under
free-living conditions, there was substantial, but not absolute,
agreement (Intraclass correlation = 0.983) between devices and the
output from the model 7164 accelerometer was significantly greater (p
< 0.01) than that of the GT3X, resulting in a 7.0% difference between
devices. The treadmill-walking conditions indicated that this
difference in output between accelerometers was based on slow-walking
speeds where there was a statistically significant (p < 0.01) and
30.3% discrepancy. 

Conclusions: The ActiGraph model 7164 and GT3X
accelerometers are not interchangeable under free-living conditions, and
the discrepancy in measurement between devices might be explained by
the difference in output under slow-walking conditions. Researchers and
clinicians should be aware of the difference in output between
generations of ActiGraph accelerometers, and perhaps other brands, in
future applications involving persons with MS and controls. 

This study looks at accelemometers, which are devices for looking at movement. These could devices could be used in trials as an outcome. This study shows that they are similar but not all the same. Prof G is test driving one at the moment, nothing like practising what you preach. 
Maybe we could have him GPSed so we would know which country he is in 🙂

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