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APPENDIX 3 - Background on statistical methods for bone densitometry reporting [ Appendix 3 Table of Contents ] STANDARD DEVIATION and COEFFICIENT OF VARIATION Precision is measured by looking at the dispersion of the repeated values around their average. If the frequency of each value is plotted against its value, a bell-shaped curve is generally obtained. This is called a gaussian distribution, and is characterised by its mean (the average value of the repeated measurements) and a parameter called standard deviation, which is a measure of the spread of the measured values. The smaller the standard deviation, the more precise is the measurement. A measured result is usually quoted in terms of its mean and standard deviation as follows: mean ± standard deviation Alternatively, the result may be quoted in terms of a percentage deviation from the mean, a parameter called the coefficient of variation. The coefficient of variation is simply the standard deviation divided by the mean, expressed as a percentage. That is: Coefficient of Variation (CV) = (Standard Deviation / Mean) x 100%
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-- This page last edited: 13 Nov 2002 -- |
