Variation exists in every measurable aspect of life, from weather to the stock exchange to sports results. It provides the topics for much of our casual conversation.
- It's 22 degrees now but it was only 3 degrees this morning.
- The stock exchange has been fluctuating wildly around 4000 points.
- How could my team win by 24 points last week and lose by 37 this week?
Variation is fundamental and directly connected to the other four big ideas.
- Expectation grows naturally out of variation (i.e. what is typical) but decisions about expectation must acknowledge underlying variation.
- Visual representation of variation is so critical that distribution demands attention.
- Variation in data is often the result of randomness; informal inference seeks to explain it.
There is further information on the fundamental ideas of variation and expectation in the article Inference as Prediction on the AAMT website.
One way to study variation in data is with graphical representations.