Frequency Distributions

Frequency Distribution

Cumulative Frequency 2

Learning objectives

• Find quartiles and calculate the interquartile range

• Estimate and interpret percentiles

Quartiles

• The range (maximum value - minimum value) shows how dispersed various data sets were

• The range affected by outlier

• The cumulative frequency graph can be divided into four equal parts, called quartiles, to get interquartile range

• Interquartile range is used to measure how spread the data was, and more representative than the range because not affected by extreme values

Example 1

• 16 students scored less than 11. Lower quartile, Q1 is 11

• 32 students scored less than 13. Median, Q2 is 13

• 48 students scored less than 15. Upper quartile, Q3 is 15

• Interquartile range (IQR) = Q3 - Q1 = 4

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