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CA Foundation · Quantitative Aptitude · Statistical Description of Data

A histogram is drawn for a continuous frequency distribution with unequal class widths. To make the heights of the rectangles correctly represent the distribution, what should be plotted on the vertical axis?

Frequency density, that is class frequency divided by class width, should be plotted. With unequal class widths the area of each rectangle must be proportional to its frequency, so raw frequencies would wrongly make wider classes look larger.

  1. ACumulative frequency of each class
  2. BClass frequency divided by class width (frequency density)Correct
  3. CClass mid-value
  4. DClass frequency multiplied by class width

Explanation

When class widths differ, the area of each rectangle must be proportional to the class frequency. This requires height = frequency / class width, called frequency density. Plotting raw frequency would exaggerate the wider classes.

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