What are variance components in gage R&R studies and Wheeler's EMP studies?

Variance components assess the amount of variation contributed by each source of measurement error, plus the contribution of part-to-part variability. The sum of the individual variance components equals the total variation. The percent contribution of the variance components is the same in gage R&R studies and in Wheeler's EMP studies.

In gage R&R, study variation (Study Var) is the amount of variation caused by the measurement system and by the differences between parts. It is calculated as 6 * the standard deviations of each source of variation.

Minitab also calculates the percent study variation (%Study Var), so that you can compare the contribution of each component to the total variation.