Welcome to this deck on histograms. We'll explore what makes them different from bar charts, especially when dealing with data grouped into classes of unequal widths. You'll learn why we use something called frequency density, and how to interpret these important charts.

Bar charts are great when all the bars have the same width. But imagine you're plotting data with unequal group sizes, like age groups of 0 to 10 years, and then 10 to 30 years. The second group is much wider. If we just use frequency for the height, the wide bar can look much more important than a narrow one, which can be very misleading.

To solve this problem, we use histograms. Instead of putting frequency on the vertical axis, we use 'frequency density'. This is a special measure that takes the width of the group, also known as the 'class width', into account. It ensures that the area of the bar, not just its height, represents the frequency.

Calculating frequency density is straightforward. The formula is: Frequency Density equals Frequency divided by Class Width. Let's repeat that: Frequency Density equals Frequency divided by Class Width.