ST6 · Spread 1 / Spread 2 / H: SD / outliers 1 / H: SD / outliers 2 Spread and standardised scores mind map

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ST6 · Spread 1 / Spread 2 / H: SD / outliers 1 / H: SD / outliers 2 Spread and standardised scores mind map

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Spread 1

Range: Range = maximum − minimum; sensitive to extremes.
Quartiles: Ordered quarters; make the chosen convention clear.
IQR: IQR describes the middle half's spread.
Percentiles: Percentile is a boundary, not a frequency at one value.

Spread 2

Inspect unusual values: Verify unusual data before removing anything.
Compare median and IQR: Compare centre and consistency together.
Transforming spread: Translation preserves spread; scaling changes it.

H: SD / outliers 1

Higher: Interpercentile ranges: Name both percentile endpoints and enclosed share.
Higher: Variance and SD: SD = square root of mean squared deviation.
Higher: Frequency SD: Weight squared values; grouped SD is estimated.
Higher: SD comparisons: Mean with SD; SD scales linearly.

H: SD / outliers 2

Higher: IQR fences: Strictly outside quartile fences flags outliers.
Higher: Three-SD rule: Outside mean ± 3SD needs investigation.
Higher: Standardised scores: Standardise distance; interpret sign and desirability.

Connections

Spread 1 → Spread 2: Quartile boundaries give the IQR used for resistant comparisons and investigation of unusual values.
H: SD / outliers 1 → H: SD / outliers 2: Standard deviation provides the distance scale for three-SD outliers and standardised scores.