Core concepts. Common traps. Built for self-study — from histograms to standard deviation.
Sum of all values ÷ count. Sensitive to outliers.
Middle value when sorted. Robust to outliers.
Value that appears most often. Can be multiple.
Max − Min. Simple measure of spread.
Q3 − Q1. Middle 50% spread. Outlier-resistant.
Below Q1 − 1.5×IQR or above Q3 + 1.5×IQR.