function sampleVariance(x) {
    if (x.length < 2) {
        throw new Error("sampleVariance requires at least two data points");
    }

    const sumSquaredDeviationsValue = sumNthPowerDeviations(x, 2);

    // this is Bessels' Correction: an adjustment made to sample statistics
    // that allows for the reduced degree of freedom entailed in calculating
    // values from samples rather than complete populations.
    const besselsCorrection = x.length - 1;

    // Find the mean value of that list
    return sumSquaredDeviationsValue / besselsCorrection;
}
The [sample variance](https://en.wikipedia.org/wiki/Variance#Sample_variance)
is the sum of squared deviations from the mean. The sample variance
is distinguished from the variance by the usage of [Bessel's Correction](https://en.wikipedia.org/wiki/Bessel's_correction):
instead of dividing the sum of squared deviations by the length of the input,
it is divided by the length minus one. This corrects the bias in estimating
a value from a set that you don't know if full.

References:
* [Wolfram MathWorld on Sample Variance](http://mathworld.wolfram.com/SampleVariance.html)

@param {Array<number>} x a sample of two or more data points
@throws {Error} if the length of x is less than 2
@return {number} sample variance
@example
sampleVariance([1, 2, 3, 4, 5]); // => 2.5