Test
Quartiles and box plots
Dynamic tasks on medians, quartiles, interquartile range, outliers and reading box-and-whisker plots.
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Sample questions
- Find the second quartile Q2: ___.
- Find the first quartile Q1: ___.
- Find the third quartile Q3: ___.
- The first quartile is ___ and the third is ___. Find the interquartile range.
- For data with Q1 = ___ and Q3 = ___, using the 1.5·IQR rule, is ___ an upper outlier?
Quartiles and box plots
For ordered data, the median Q2 divides the values into two parts, while Q1 and Q3 divide them into quarters. The interquartile range IQR = Q3 − Q1 measures the spread of the middle 50% and is less sensitive to extreme values than the full range.
Plots and outliers
A box plot displays the minimum, Q1, median, Q3 and maximum, with outliers shown separately under the chosen convention. A common outlier rule is below Q1 − 1.5IQR or above Q3 + 1.5IQR. Compare both centre and spread when interpreting groups.
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