What is variance?

Variance is like how much your toys differ from one day to the next, some days you have all your favorite ones, other days you’re stuck with just a few.

Imagine you and your friend both get candy every day after school. Sometimes you get 5 pieces, sometimes 3, sometimes even 7. Your friend gets exactly 4 pieces every single day. That means your candy is more different each day, it has more variance, while your friend’s is more consistent, with less variance.

Let’s say you track how many candies you get for a week:

5, 3, 7, 4, 6.

To find the variance, we first figure out the average (or mean) of your candy, that would be around 5 candies.

Then we see how far each day's amount is from this average:

• 5 is exactly on target
• 3 is 2 below
• 7 is 2 above
• 4 is 1 below
• 6 is 1 above

We square those differences (so they’re all positive), add them up, and divide by the number of days, that gives us a measure of variance. The bigger the numbers, the more your candy amount fluctuates, like when you get super excited on some days and barely get any on others! Variance is like how much your toys differ from one day to the next, some days you have all your favorite ones, other days you’re stuck with just a few.

Imagine you and your friend both get candy every day after school. Sometimes you get 5 pieces, sometimes 3, sometimes even 7. Your friend gets exactly 4 pieces every single day. That means your candy is more different each day, it has more variance, while your friend’s is more consistent, with less variance.