What term describes the square sum of the differences of the relative crystal efficiencies between two scans?

The correct choice for describing the square sum of the differences of the relative crystal efficiencies between two scans is 'Sum of Squares.'

The Sum of Squares is a fundamental concept in statistics, used to measure the variation or dispersion of a dataset. It involves calculating the difference between each data point and the mean, squaring those differences to eliminate any negative values, and then summing them together. In the context of evaluating relative crystal efficiencies in PET scans, this term would reflect how much the efficiencies deviate from the average or expected value, calculated by summing the squares of these differences.

Understanding the context of the question is crucial because while "Average Variance" and "Standard Deviation" also deal with variability in data, they do so in different ways. The Average Variance typically refers to the average of the squared differences and is computed after determining how the data points collectively disperse around the mean, rather than directly summing the squares. Standard Deviation offers a measure of dispersion that reflects how data varies around the mean, but it is derived from the variance.

"Variance Ratio" usually refers to the comparison or ratio of variances between different datasets. It is not relevant in this context, where we are specifically interested in the accumulated squared differences