Variation tells you how bumpy the road is. Standard deviation (SD) captures bumps everywhere; the IQR focuses on the middle 50%. When life is skewed (lateness, income, completion time), IQR is a steadier compass: it ignores the cliffs and measures the lane. Say it plainly: “Half of students finished between 12–16 minutes (IQR = 4).” Guardrails don’t solve the trip, but they keep you from arguing about the ditch. Use SD when the whole spread matters. Use IQR when you need a reliable middle to plan around.
