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Compute bilateral symmetry index

Source: R/biomech-com.R
symmetryIndex.Rd

Calculates a symmetry index between left and right side measurements using standard methods from the biomechanics literature.

Usage

symmetryIndex(left, right, method = "robinson")

Arguments

left

Numeric vector or matrix of left-side values.

right

Numeric vector or matrix of right-side values (same dimensions as left).

method

Character string specifying the symmetry index method. "robinson" (default): Robinson (1987) symmetry index \(SI = |L - R| / (0.5 \times (L + R)) \times 100\). "ratio": simple ratio \(L / R\).

Value

For vectors, a numeric vector of symmetry indices. For matrices, row-wise symmetry indices (a numeric vector of length equal to nrow(left)).

Details

The Robinson (1987) symmetry index returns 0 for perfect symmetry and larger values for greater asymmetry. It is expressed as a percentage. The ratio method returns 1.0 for perfect symmetry.

References

Robinson, R.O., Herzog, W., & Nigg, B.M. (1987). Use of force platform variables to quantify the effects of chiropractic manipulation on gait symmetry. Journal of Manipulative and Physiological Therapeutics, 10(4), 172-176.

See also

calculateStepSymmetry() for gait-specific symmetry metrics, plotSymmetry() for symmetry visualization, calculateGaitParameters() for comprehensive gait analysis.

Examples

# Perfect symmetry
symmetryIndex(10, 10)   # returns 0
#> [1] 0

# Known asymmetry
symmetryIndex(10, 8)    # returns ~22.2%
#> [1] 22.22222

# Ratio method
symmetryIndex(10, 8, method = "ratio")  # returns 1.25
#> [1] 1.25