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

JOURNAL OF BIOMECHANICS

卷:48

Article

Pataky, Todd C.¹  Vanrenterghem, Jos²  Robinson, Mark A.² 

[1] Shinshu Univ, Dept Bioengn, Matsumoto, Nagano, Japan

[2] Liverpool John Moores Univ, Res Inst Sport & Exercise Sci, Liverpool L3 5UX, Merseyside, England

关键词: Kinematics;    Statistical parametric mapping;    Random field theory;    Time series analysis;   

DOI  :  10.1016/j.jbiomech.2014.10.013

来源: Elsevier

【 摘 要 】

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 non-phasic 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 effect) and a main-effects-only model. In both models the main effect of PAIN failed to reach significance at alpha=0.05. The main effect of GENDER reached significance over 5-40% stance (p=0.0005), but only for the full model. The interaction effect (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 effect 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. (C) 2014 Elsevier Ltd. All rights reserved.

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