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    Dear all,

    I'd like to agree very much with Chris's comments. From deep within
    clinical gait analysis my assumption is that the methods we use are
    reasonably accurate for the populations we are examining. However I do not
    know. The applied biomechanics community has been negligent to an
    extraordinary degree in not specifying the validity of its results. Most
    labs produce "normal databases" which give some indication of repeatability
    of data (generally taken from a population other than the one they are
    working with). These studies however give no information about the validity
    of the data. Hidden in the academic literature are a variety of studies
    which throw some light on various aspects of our modelling but these
    generally stay there. Errors occur, and are unspecified at all levels of
    data capture and processing. Try pressing an equipment manufacturer for a
    specification of the accuracy of marker detection - and then put it to the
    test in a real lab!

    To my mind the most pressing need for clinical biomechanics is the
    development of measures of validity. Without these we don't know which
    data is valid and which is not. Without this information it is also
    impossible to know which measurements we can accept and which we to
    development further. I am convinced that within the dataset we use some
    data are reliable and some are not. I have my instincts as an engineer to
    try and determine which are which, but I have very little hard data to
    support this. Persuading clinicians to place less emphasis on some data
    than on others as a consequence of measurement/modelling methodologies is
    virtually impossible in the absence of a clear indication of the validity
    of the various measures.

    Of course there is a methodological problem here in that to assess the
    validity of one model it is generally necessary to have another model that
    one believes to be a close match to reality. It may be that Prof Hatze's
    call for the development of new generation of models is the precursor to
    understanding the existing models. There are however other methods of
    assessing validity of existing models, from sensitivity analysis to input
    parameters to good old fashioned informed discussion of likely error
    sources. Can I suggest that what the clinical biomechanics community
    requires is to drag this discussion out of the academic back room and into
    the forefront of its considerations.

    Of course we have to discuss this in context. The one thing we know less
    about than the validity of our data is how to use them once we've got them.
    Its easy to get depressed by the limitations of our own techniques but,
    with the possible exception of transverse plane kinematics, I'm happy that
    the data we supply to clinicians are appropriate for their level of
    understanding of how to interpret those data in clinical decision making.

    This probably reveals a tension which is present in any applied science.
    The most pressing need I see for coming years is not for more complex
    models but for the appropriate incorporation into clinical practice of the
    models that we already have. I am generally fairIy depressed by the level
    of biomechanical understanding I see from both bioengineers and clinical
    colleagues at conferences, in peer reviewing publications and in clinical
    audit. There is still a huge amount that first generation biomechanics has
    to offer the clinical community on top of what it offers at present. I can,
    however, quite understand those who see biomechanics as a discipline in its
    own right and want to pioneer the second generation. The tension between
    pure and applied aspects of any discipline is positive. Let the purists
    pioneer the second generation, but lets all concentrate on applying the
    first generation appropriately at the same time.

    Richard Baker

    Richard Baker PhD CEng
    Gait Analysis Service Manager and Director of Research
    Hugh Williamson Gait Laboratory
    Royal Children's Hospital
    Flemington Road,
    Victoria 3052, Australia

    Tel: +61(0)3 9345 5354
    Fax: +61(0)3 9345 5447

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