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Two-way ANOVA for scalar trajectories, with experimental evidence of non-phasic interactions

Pataky, TC and Vanrenterghem, J and Robinson, MA (2015) Two-way ANOVA for scalar trajectories, with experimental evidence of non-phasic interactions. JOURNAL OF BIOMECHANICS, 48 (1). pp. 186-189. ISSN 0021-9290

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Abstract

Kinematic and force trajectories are often normalized in time, with mean and variance summary statistic trajectories reported. It has been shown elsewhere, for simple one-factor experiments, that statistical testing can be conducted directly on those summary statistic trajectories using Random Field Theory (RFT). This technical note describes how RFT extends to two-factor designs, and how bizarre “nonphasic interactions” can occur in multi-factor experiments. We reanalyzed a public dataset detailing stance phase knee flexion during walking in (a) patellofemoral pain vs. controls, and (b) females vs. males using both a full model (with interaction e↵ect) and a main-e↵ects-only model. In both models the main e↵ect of PAIN failed to reach significance at ↵=0.05. The main e↵ect of GENDER reached significance over 5–40% stance (p=0.0005), but only for the full model. The interaction e↵ect (in the full model) reached significance over 0–15% of stance (p=0.030), and resulted from greater flexion in females but decreased flexion in males in PFP vs. controls. Thus there was a non-phasic interaction, in which a non-significant interaction (over 20–40% stance) suppressed the main e↵ect of GENDER. Similarly, if we had only analyzed 20–40% stance, we would have committed Type II error by failing to reject the null PAIN-GENDER interaction hypothesis. The possible presence of non-phasic interactions implies that trajectory analyses must be conducted at the whole-trajectory level, because a failure to do so will generally miss non-phasic interactions if present.

Item Type: Article
Additional Information: NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Biomechanics. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Biomechancis 48(1), Jan 2015 DOI:10.1016/j.jbiomech.2014.10.013
Uncontrolled Keywords: 0903 Biomedical Engineering, 1106 Human Movement And Sports Science, 0913 Mechanical Engineering
Subjects: R Medicine > RC Internal medicine > RC1200 Sports Medicine
Divisions: Sport & Exercise Sciences
Publisher: Elsevier
Related URLs:
Date Deposited: 30 Apr 2015 15:06
Last Modified: 15 Nov 2015 00:50
DOI or Identification number: 10.1016/j.jbiomech.2014.10.013
URI: http://researchonline.ljmu.ac.uk/id/eprint/970

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