Standard Deviation
Standard deviation is a number that tells you how spread out a group of values are from their average.
Think of baking cookies. If all your cookies come out nearly the same size, the standard deviation is small. If some are huge and some are tiny, the standard deviation is large.
Explaining standard deviation by grade level
Think about timing a bus on the same road each day. Some days it takes ten minutes. Other days it takes twelve or eight. Standard deviation tells you how much those times jump around from the middle.
Projects that explore standard deviation
Standard deviation measures how far individual data points sit from the group average — it sets the boundary for what counts as normal random variation. In this project, you compare real baseball streak counts to artificial seasons built on chance alone. If real streaks fall more than two standard deviations from the model’s average, you can say with 95% confidence that something beyond luck is shaping the results.
How consistent is a bus route from one day to the next? This project answers that by measuring travel time per kilometer for each segment over many rides. Single-lane segments show the widest variation — up to 418%. A high standard deviation for those segments means individual rides swing far from the average, signaling unpredictable traffic conditions.