Averaging Trials Versus Averaging Trial Peaks: Impact on Study Outcomes

in Journal of Applied Biomechanics
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Gait data are commonly presented as an average of many trials or as an average across participants. Discrete data points (eg, maxima or minima) are identified and used as dependent variables in subsequent statistical analyses. However, the approach used for obtaining average data from multiple trials is inconsistent and unclear in the biomechanics literature. This study compared the statistical outcomes of averaging peaks from multiple trials versus identifying a single peak from an average profile. A series of paired-samples t tests were used to determine whether there were differences in average dependent variables from these 2 methods. Identifying a peak value from the average profile resulted in significantly smaller magnitudes of dependent variables than when peaks from multiple trials were averaged. Disagreement between the 2 methods was due to temporal differences in trial peak locations. Sine curves generated in MATLAB confirmed this misrepresentation of trial peaks in the average profile when a phase shift was introduced. Based on these results, averaging individual trial peaks represents the actual data better than choosing a peak from an average trial profile.

Dames is with the Kinesiology Department, State University of New York Cortland, Cortland, NY, USA. Smith and Heise are with the School of Sport & Exercise Science, University of Northern Colorado, Greeley, CO, USA.

Address author correspondence to Kevin D. Dames at kevin.dames@cortland.edu.
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