When working with data we tend to ask ourselves two big questions:
1. What "typical" value could we use to describe this data?
To descirbe the "center" of the data we usually use either the mean (for symmetrical data) or the median (for skewed data).
2. How accurate or spread out is this data?
We use the word variability to describe how spread the data is. The more spread out the data is the less reliable it is. We can calculate how variable data is using two different methods: interquartile range (for skewed data) and standard deviation (for symmetrial data).
Interquartile Range is exactly what the name suggests:
Interquartile Range
(inside) (quarters) (big - little)
It is the range of the inside quartiles (or the range of just the box in a box plot).
Q3 - Q1 = IQR
We use this value to explain how variable (spreak out) our data is and to justify why it is good data. The smaller the IQR the more reliable your data is!