Thus a two-tailed test would be used if the alternative hypothesis were that two quantities are unequal, without prior specification of which is larger. Synonymous with nondirectional test. The researcher's data-based decision that the null hypothesis is false when it is really true. This incorrect conclusion is not the result of a mistake in the analysis. While this incorrect conclusion could be the result of bad luck as in the case of a Type I Error, a more worrisome possibility is that the experiment had low power.
Variance is a formal measure of the dispersion, or scatter, among the numbers in a set of data.
The variance is a weighted average of the differences between the numbers, with larger discrepancies contributing more heavily. Dividing the sum by n - 1 accomplishes the averaging. Since data always should be regarded as sample values, this is the appropriate definition in an empirical field.