A topic in the Open Knowledge Graph — a free, open map of 15,290 topics and the order to learn them in.
Mean, median, and mode are three measures of central tendency -- ways to describe the "center" or "typical value" of a data set. The mean (average) is the sum of all values divided by the count. The median is the middle value when data is ordered from least to greatest (or the average of the two middle values for even-sized sets). The mode is the most frequently occurring value. Each measure tells a different story: the mean is sensitive to outliers, the median is resistant to them, and the mode identifies the most common value. Understanding when each is most appropriate is as important as computing them.
Use physical models: stack unifix cubes to represent data values, then "level out" by redistributing cubes equally (this shows the mean). Order values and find the middle (median). Identify repeats (mode). Discuss data sets where the three measures disagree: "The mean salary at this company is $100,000, but the median is $50,000 -- why?" This builds critical thinking about which measure to trust.
When you have a list of numbers — test scores, temperatures, heights — you often want a single number that captures "what is typical." Mean, median, and mode are three different answers to that question, and each is best suited to different situations.
The mean (average) treats all values equally: add them up and divide by the count. It is the "fair share" value — if you redistributed everything evenly, each person would get the mean. The problem is that very large or very small values (called outliers) pull the mean toward them. If nine friends each have $10 and one friend has $1,000, the mean is $109 — but that is not what anyone actually has.
The median sidesteps this problem by finding the middle value after ordering the data. Half the values are below the median, half are above. Because it only looks at position (not magnitude), an extreme outlier barely budges it. This is why economists report median household income rather than mean income: a small number of billionaires would make the mean look far higher than what a typical family earns.
The mode is simply the most frequent value. It is the only measure that works for non-numeric data — the most popular shirt color, the most common answer on a survey. For numerical data, it is most useful when values cluster strongly at a few points (like shoe sizes), but it can be misleading or absent when every value is unique.
Knowing which measure to use is as important as computing them correctly. Always ask: does my data have outliers? If yes, prefer the median. Is my data categorical? Use the mode. Do I need to account for every value proportionally? Use the mean. The three measures often agree in symmetric, well-behaved data sets — but precisely when they disagree is when you need to think carefully about which one to report.