Stats - Histograms | Olly Britton

Bar charts versus histograms

What sort of data do you normally use bar charts with?

Discrete data.

What sort of data do you normally use histograms with?

Continuous data.

At GCSE, what was the frequency in a histogram?

The area of a column.

Why is the GCSE definition of a histogram incorrect at A-level?

The area of the bars is not always frequency; it can be scaled by a scaling factor.

If the frequency reads $30$ from a table, but is $60$ on a histogram, what is the scaling factor?

\[\frac{60}{30} = 2\]

What is a frequency polygon?

A histogram where you draw a line from the midpoint of each interval at the top of a bar.

In a frequency polygon, how should you deal with there being no column for a group of frequencies?

Make the line touch the $x$-axis.