Interpreting Histograms

Interpreting Histogramsvideo

Interpreting histograms

How do I interpret a histogram?

• It is important to remember that the frequency density (y-) axis does not tell us frequency

  • The area of the bar is equal to the frequency

    • $\begin{array}{rcl}\mathrm{frequency}& =& \mathrm{frequency} \mathrm{density}\times \mathrm{class} \mathrm{width}\end{array}$

• Note that a very simple histogram may have equal class widths

  • In this case the y-axis may be labelled 'frequency' instead of 'frequency density'

  • If 'frequency' is on the y-axis, then you can use the heights of the bars to directly determine the frequencies

• You may be asked to estimate the frequency of part of a bar/class interval within a histogram

  • Find the area of the bar for the part of the interval required

  • Once area is known, frequency can be found as above

• You can use histograms for two data sets to compare the data distributions

  • but only if they have the same class intervals and the same frequency density scales