Final answer:
The expression Σ(X-μ) denotes the sum of all deviations of data points from the population mean, which is used in the process of calculating the standard deviation, a key measure of variability in a dataset.
Step-by-step explanation:
In statistics, the expression Σ(X-μ) stands for the sum of deviations of individual data points (X) from the population mean (μ). This expression is used to calculate the standard deviation, which is a measure of the dispersion of a set of data from its mean. If X represents individual values of a random variable, and μ is the population mean, each value of X-μ represents a deviation. Summing all these deviations (Σ(X-μ)) is often a step in calculating measures of variability like the variance or standard deviation. However, this sum will always be zero because deviations above the mean will cancel out those below the mean.
To calculate standard deviation, one typically squares these deviations to get rid of the negative signs, sums these squared deviations (Σ(X-μ)2), and then takes the square root after dividing by the number of data points (or by n-1 if working with a sample rather than a population).