The importance of addressing heteroscedasticity in the reliability analysis of ratio‐scaled variables: an example based on walking energy‐cost measurements

Aim  When analysing the reliability of ratio‐scaled variables, such as walking energy cost, variability of the error term often increases with increasing mean values. This phenomenon is called heteroscedasticity, and it makes the analysis of reliability more complicated. This study presents an examination of heteroscedasticity for walking energy cost before analysing the reliability.

[1]  M. Schwartz,et al.  Variability and minimum detectable change for walking energy efficiency variables in children with cerebral palsy , 2009, Developmental medicine and child neurology.

[2]  M. Schwartz,et al.  Walking energy expenditure in able-bodied individuals: a comparison of common measures of energy efficiency. , 2009, Gait & posture.

[3]  S. le Cessie,et al.  A practical approach to Bland-Altman plots and variation coefficients for log transformed variables. , 2008, Journal of clinical epidemiology.

[4]  Jaap Harlaar,et al.  Methodological considerations for improving the reproducibility of walking efficiency outcomes in clinical gait studies. , 2008, Gait & posture.

[5]  J. Harlaar,et al.  Reproducibility evaluation of gross and net walking efficiency in children with cerebral palsy , 2006, Developmental medicine and child neurology.

[6]  D. Knol,et al.  The combined effect of lower-limb multilevel botulinum toxin type a and comprehensive rehabilitation on mobility in children with cerebral palsy: a randomized clinical trial. , 2006, Archives of physical medicine and rehabilitation.

[7]  M. Schwartz,et al.  A nondimensional normalization scheme for oxygen utilization data. , 2006, Gait & posture.

[8]  Jon R. Davids,et al.  The Treatment of Gait Problems in Cerebral Palsy , 2005 .

[9]  M. Pierrynowski,et al.  Physical activity level is associated with the O2 cost of walking in cerebral palsy. , 2005, Medicine and science in sports and exercise.

[10]  J Harlaar,et al.  Validation of the portable VmaxST system for oxygen-uptake measurement. , 2004, Gait & posture.

[11]  Brian T. Smith,et al.  Energy cost of walking in children with cerebral palsy: relation to the Gross Motor Function Classification System , 2004, Developmental medicine and child neurology.

[12]  Stefania Fatone,et al.  High‐ or low‐technology measurements of energy expenditure in clinical gait analysis? , 1999, Developmental medicine and child neurology.

[13]  J. Richards,et al.  Variability of energy-consumption measures in children with cerebral palsy. , 1998, Journal of pediatric orthopedics.

[14]  A. Nevill,et al.  Assessing agreement between measurements recorded on a ratio scale in sports medicine and sports science. , 1997, British journal of sports medicine.

[15]  A. Nevill,et al.  Why the analysis of performance variables recorded on a ratio scale will invariably benefit from a log transformation. , 1997, Journal of sports sciences.

[16]  D G Altman,et al.  Statistics Notes: Measurement error proportional to the mean , 1996, BMJ.

[17]  Douglas G. Altman,et al.  Statistics Notes: Transforming data , 1996 .

[18]  R. Waters,et al.  Energy‐speed relationship of walking: Standard tables , 1988, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[19]  D. Altman,et al.  STATISTICAL METHODS FOR ASSESSING AGREEMENT BETWEEN TWO METHODS OF CLINICAL MEASUREMENT , 1986, The Lancet.

[20]  J. Campbell,et al.  Energetics of walking in cerebral palsy. , 1978, The Orthopedic clinics of North America.

[21]  A. Beckett,et al.  AKUFO AND IBARAPA. , 1965, Lancet.

[22]  H. Ralston.  Energy-speed relation and optimal speed during level walking , 1958, Internationale Zeitschrift für angewandte Physiologie einschließlich Arbeitsphysiologie.

[23]  D. Morgan,et al.  Within- and between-day stability of treadmill walking VO2 in children with hemiplegic cerebral palsy. Stability of walking VO2 in children with CP. , 2005, Gait & posture.

[24]  G Atkinson,et al.  Statistical Methods For Assessing Measurement Error (Reliability) in Variables Relevant to Sports Medicine , 1998, Sports medicine.

[25]  J M Bland,et al.  Transforming data. , 1996, BMJ.

[26]  J. Lovejoy,et al.  Energy expenditure. , 1996, Endocrinology and metabolism clinics of North America.