Which symbol denotes the mean of a population variable?

• A. x̄
• B. μ
• C. N
• D. Σ

Answer: (B)

The symbol for the average of an entire population is μ, used to denote a population parameter. This Greek letter stays fixed for the whole population and represents the true mean. In contrast, the bar over x, written x̄, is used for the sample mean—the average calculated from a subset of data and which can vary from one sample to another. The letter N stands for the population size, not a mean, and the summation symbol Σ stands for summing values, often used in formulas to compute the mean but not by itself denoting the mean. For example, with population values 2, 4, and 6, the population mean is μ = (2 + 4 + 6) / 3 = 4. If you take a sample and compute its mean, you get x̄ = (sum of sample values) / (sample size). So the mean of a population variable is denoted by μ.