Mean

The arithmetic average: sum all values and divide by count. The most commonly used summary statistic and often the most misleading one. The mean is mathematically useful (it's the expected value of a random draw from the distribution) but psychologically deceptive when distributions are skewed. When Jeff Bezos walks into a bar, the average net worth of everyone in the bar becomes billions—a meaningless number that describes nobody. Yet most business reporting defaults to averages, creating systematically distorted pictures.

When to use it

When evaluating any summary statistic presented as an 'average'; when the underlying distribution might be skewed (income, company sizes, customer values, response times—most business distributions are skewed); when making forecasts based on historical averages; when communicating data to decision-makers.

How it can help

Whenever presented with an average, ask two questions: (1) Is the distribution symmetric or skewed? If skewed, the mean is misleading. (2) What's the standard deviation? An average without variance is like a map without scale. 'Average customer LTV is $500' could mean everyone is near $500 (useful!) or that most are $50 and a few are $5,000 (very different strategy implications). Always request the median alongside the mean, and the full distribution when possible.