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SOCIAL STATISTICS

Renáta Németh, Dávid Simon

ELTE

Frequency polygon

Frequency polygon

Appropriate for interval-ratio variables

The above data again:

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The frequency polygon shows the differences in frequencies or percentages among classes of the categories of an interval-ratio variable. Points representing the frequencies of each class are placed above the midpoint of the class and are joined by a straight line.

It is similar to the histogram; differences:

  • fix width of intervals

  • percentages (or frequencies) are assigned to the midpoint of the interval

Example: In a reaction time trial time is the variable measured, which is interval-ratio. Frequency distribution of a classification is shown in the table below:

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More easily readable when presented graphically (width is fixed at 5, the first and the last class is defined as 20-25 and 55-60, respectively):

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