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Related Experiment Videos

Quantifying asymmetry: ratios and alternatives.

Erin M Franks1, Luis L Cabo

  • 1Department of Biological Sciences, The University of Notre Dame, Notre Dame, IN, 46556.

American Journal of Physical Anthropology
|May 21, 2014
PubMed
Summary

Traditional methods for studying skeletal asymmetry using ratios are flawed. This study reveals that multivariate analyses offer a more accurate approach to assessing asymmetry in human bones.

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Area of Science:

  • Anthropometry
  • Bioengineering
  • Human Anatomy

Background:

  • Metric skeletal asymmetry studies traditionally use univariate analyses and ratio transformations to control for size.
  • This
  • controlling for size
  • approach aims to create size-free asymmetry indices by dividing raw asymmetries by a size marker.
  • However, ratio transformations often violate the assumption of isometry, potentially obscuring true asymmetries and producing spurious results.

Purpose of the Study:

  • To evaluate the effectiveness of classic ratio-based indices in detecting and characterizing asymmetry patterns in four human appendicular bones.
  • To explore and propose alternative methodological approaches for analyzing skeletal asymmetry.

Main Methods:

Keywords:
antisymmetryasymmetry indicesdirectional asymmetryfluctuating asymmetry

Related Experiment Videos

  • The study examined the performance of traditional ratio indices on four human appendicular bones.
  • Exploratory multivariate techniques, including Principal Components Analysis (PCA).
  • Confirmatory linear methods such as regression and analysis of covariance were employed.

    • Main Results:

    • The classic ratio model was found to be inadequate for controlling size in the examined bones, as numerator and denominator variables were independent.
    • Ratio transformations introduced significant biases, leading to spurious asymmetry patterns when comparing different elements and variables.
    • Multivariate analyses indicated that size and range transformations should precede asymmetry calculations.

    Conclusions:

    • The traditional ratio-based method for analyzing skeletal asymmetry is unreliable and can generate misleading results.
    • Multivariate techniques, combined with linear methods, provide a more robust and accurate alternative for assessing skeletal asymmetry.
    • Size and range adjustments should be implemented prior to calculating asymmetry indices for more valid comparisons.