Response to letter to the editor regarding "Application of principal component analysis in clinical gait research".

Bernstein, N.A. 1967. The Co-ordination and Regulation of Movements, Pergamon Press. Boyer, K.A., Angst, M.S., Asay, J., Giori, N.J., Andriacchi, T.P., 2012. Sensitivity of gait parameters to the effects of anti‐inflammatory and opioid treatments in knee osteoarthritis patients. J. Orthop. Res. 30 (7), 1118–1124. Comrey, A., Lee, H., 1992. A First Course in Factor Analysis. Erlbaum, Hillsdale, NJ. Federolf, P.A., Boyer, K.A., Andriacchi, T.P., 2013. Application of principal component analysis in clinical gait research: identification of systematic differences between healthy and medial knee-osteoarthritic gait. J. Biomech. 46 (13), 2173–2178. Harrison, A.J., Ryan, W., Hayes, K., 2007. Functional data analysis of joint coordination in the development of vertical jump performance. Sports Biomech./Int. Soc. Biomech. Sports 6 (2), 199–214. Huber, P., 1981. Robust Statistics, 1st ed. Wiley, New York. MacCallum, R., Widaman, K., Zhang, S., Hong, S., 1999. Sample size in factor analysis. Psychol. Methods 4, 84–89. Nunnally, J.C., 1987. Psychometric Theory, 2nd ed. McGraw Hill, New York. Richter, C., O'Connor, N.E., Marshall, B., Moran, K., 2014. Analysis of characterizing phases on waveforms – an application to vertical jumps. J. Appl. Biomech. (in press), PMID: 24042053.

[1]  Andreas Daffertshofer,et al.  PCA in studying coordination and variability: a tutorial. , 2004, Clinical biomechanics.

[2]  B. Price.  A First Course in Factor Analysis , 1993 .

[3]  Noel E. O’Connor,et al.  Analysis of characterizing phases on waveform: an application to vertical jumps. , 2014, Journal of applied biomechanics.

[4]  A.J. Harrison,et al.  Functional data analysis of joint coordination in the development of vertical jump performance , 2007, Sports biomechanics.

[5]  J. L. Astephen,et al.  Biomechanical features of gait waveform data associated with knee osteoarthritis: an application of principal component analysis. , 2007, Gait & posture.

[6]  R. Sitgreaves.  Psychometric theory (2nd ed.). , 1979 .

[7]  V. von Tscharner,et al.  Subspace Identification and Classification of Healthy Human Gait , 2013, PloS one.

[8]  Katherine A Boyer,et al.  Repeatability of gait analysis for measuring knee osteoarthritis pain in patients with severe chronic pain , 2013, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[9]  N. Troje.  Decomposing biological motion: a framework for analysis and synthesis of human gait patterns. , 2002, Journal of vision.

[10]  Benno M Nigg,et al.  Marker-based classification of young–elderly gait pattern differences via direct PCA feature extraction and SVMs , 2013, Computer methods in biomechanics and biomedical engineering.

[11]  Howard B. Lee,et al.  A first course in factor analysis , 1973 .

[12]  T. Andriacchi,et al.  Application of principal component analysis in clinical gait research: identification of systematic differences between healthy and medial knee-osteoarthritic gait. , 2013, Journal of biomechanics.

[13]  Peter Andreas Federolf,et al.  A Novel Approach to Solve the “Missing Marker Problem” in Marker-Based Motion Analysis That Exploits the Segment Coordination Patterns in Multi-Limb Motion Data , 2013, PloS one.

[14]  Jos Vanrenterghem,et al.  Vector field statistical analysis of kinematic and force trajectories. , 2013, Journal of biomechanics.

[15]  Kazuyoshi Takayama,et al.  Holographic interferometric visualization of the Richtmyer-Meshkov instability induced by cylindrical shock waves , 1999 .

[16]  R. MacCallum,et al.  Sample size in factor analysis. , 1999 .

[17]  J. Nunnally.  Psychometric Theory (2nd ed), New York: McGraw-Hill. , 1978 .

[18]  T P Andriacchi,et al.  Kinematic adaptations to a variable stiffness shoe: mechanisms for reducing joint loading. , 2012, Journal of biomechanics.

[19]  K. Deluzio,et al.  Knee biomechanics of moderate OA patients measured during gait at a self-selected and fast walking speed. , 2007, Journal of biomechanics.

[20]  Benno M Nigg,et al.  Shoe midsole hardness, sex and age effects on lower extremity kinematics during running. , 2012, Journal of biomechanics.

[21]  Lorenzo Chiari,et al.  Human movement analysis using stereophotogrammetry. Part 4: assessment of anatomical landmark misplacement and its effects on joint kinematics. , 2005, Gait & posture.

[22]  J. Marron,et al.  PCA CONSISTENCY IN HIGH DIMENSION, LOW SAMPLE SIZE CONTEXT , 2009, 0911.3827.