Statistics · Data presentation
Chapter 1 · 3
The idea
Measures of spread, standard deviation and coding
Range, interquartile and interpercentile range, and — the big one — variance and standard deviation from sums Σx and Σx² (and Σfx, Σfx²). Plus coding: how a linear change of variable rescales the mean and standard deviation, and how to decode back to the original data.
A full journey — read it, play with it, work it, then earn real exam marks. Everything stays on the timeline below.
In this lesson — start anywhere
Statistics · Data presentation
Measures of spread, standard deviation and coding
Range, interquartile and interpercentile range, and — the big one — variance and standard deviation from sums Σx and Σx² (and Σfx, Σfx²). Plus coding: how a linear change of variable rescales the mean and standard deviation, and how to decode back to the original data.
Why it works
How scattered is it?
A measure of location tells you where the data sits; a measure of spread tells you how scattered it is. Two data sets can share a mean yet be wildly different — spread is what separates them.The simple ranges.
- Range largest smallest. Quick, but ruined by a single outlier.
- Interquartile range — the spread of the middle , so it ignores the extreme quarters and resists outliers.
- Interpercentile range — e.g. the to range, .
Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
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