Stats 1.4The video for this lesson is on its way.
Everything else is ready: study the parts, the key terms and the quiz below.
- Part 11Similar means, different invoice values
- Part 22Build sample variance from deviations
- Part 33Return to pounds with standard deviation
- Part 44Measure the middle half with quartiles
- Part 55Test one invoice's influence
- Part 66Report what these groups support
- Part 77Reproduce and challenge the calculation
Stats 1.4Concept7 parts
Variance, Standard Deviation and IQR
Measure spread, robustly when the data has outliers.
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In this lesson7 parts
- 01Similar means, different invoice values
- 02Build sample variance from deviations
- 03Return to pounds with standard deviation
- 04Measure the middle half with quartiles
- 05Test one invoice's influence
- 06Report what these groups support
- 07Reproduce and challenge the calculation
Key terms
The words this lesson introduces, each in one line. The module’s glossary collects them all.
- spread
- How far observed values extend around a stated center.
- deviation
- An observed value minus its group's mean.
- squared deviation
- The square of an observed value minus the group mean.
- sample variance
- The sum of squared deviations divided by
n - 1. Its unit is the original unit squared. - sample standard deviation
- The square root of the sample variance, in the original unit.
- quartile
- A value dividing ordered observations at 25%, 50% or 75% under a stated method (NumPy and pandas interpolate linearly by default).
- IQR
- The third quartile minus the first quartile: the spread of the middle half.
- sensitivity check
- Recompute after one stated change and compare the results.
Quiz 5 questions
Your first pick on each question is the one that counts, and a right one earns a coin. Getting one wrong here is how the lesson sticks.
Practice
Problems to solve in your own notebook. Each states the problem, not the steps: working out the steps is the exercise. Level A applies the lesson, B combines it with earlier ones, C stretches it.
The self-checking notebook for this lesson is Invoice centre and spread.
Common mistakes
What you will see when it goes wrong, why it happens, and the fix.
Where it’s used
Where this lesson’s ideas turn up in real work.