Quick questions on Univariate descriptive statistics: tables, histograms, ogives, mean and standard deviation, the five-number summary, box plots and outliers

3short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is outliers by the 1.5 IQR rule?

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An outlier is a reading that sits unusually far from the rest. The standard criterion in this course is based on the IQR: a value is an outlier if it lies more than

1.5 \times \text{IQR}

below

Q_1

or more than

1.5 \times \text{IQR}

above

Q_3

. The two cut-offs

What are comparing distributions with parallel box plots?

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To compare two groups, draw their box plots on a common scale, one above the other: a parallel box plot. You compare centre (median against median), spread (IQR and range), and shape (skew and outliers). Below are daily rainfall totals on

11

wet days in two suburbs (in millimetres). North is

6, 8, 9, 11, 12, 14, 15, 17, 19, 22, 40

; South is

10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21

What is not ordering the data first?

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The median and quartiles are positions in the ordered list. Working on the raw, unordered list gives nonsense.

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