Spread & Variability
Range and interquartile range
Start with the basics and progress through 3 lessons. Each lesson builds on the previous one.
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Test Your Knowledge
10 questions, new mix each time (from 45)
In This Topic (3 lessons)
Range and Interquartile Range
Learn how to measure the spread of data using range and IQR.
Standard Deviation
Learn how to measure data spread using standard deviation and understand what it tells you about a data set.
Calculating Standard Deviation
Master the step-by-step process of calculating standard deviation for any data set.
Range and spread describe how data is distributed. While central tendency tells where data clusters, spread tells how far values deviate from the center. Understanding range, variance, standard deviation, and interquartile range helps assess data variability.
What You'll Learn
- Calculate range of a dataset
- Find variance and standard deviation
- Calculate interquartile range
- Interpret spread in context
- Compare spread across datasets
Frequently Asked Questions
What is the difference between range and IQR?
Range is maximum minus minimum (affected by outliers). IQR (interquartile range) is Q3 minus Q1, measuring spread of the middle 50% (resistant to outliers).
What does standard deviation tell us?
Standard deviation measures average distance from the mean. Small SD means data clusters tightly; large SD means data is spread out.
When should I use IQR instead of standard deviation?
Use IQR when data has outliers or is skewed. Standard deviation assumes somewhat symmetric data and is affected by extreme values.