WJEC Maths for AS: Applied sample

2 Data presentation and interpretation 18 Bar charts are useful to compare data for two different variables like this Dog 80 70 60 50 40 30 20 10 0 Cat Guinea pig Rabbit Budgie Mouse Gerbil Parrot Hamster Fish Other animal Other bird Reptile Area A Area B Frequency The main features of bar charts are: • There are gaps between the bars for single variable bar charts. • There are usually categories on one axis and frequency on the other. • The height of the bar represents the frequency. Histograms On ϐirst impressions, histograms look like bar charts but there are some important differences: • There are gaps between the bars (or groups of bars) in bar charts but in histograms there are no such gaps. • There are numbers on both sets of axes – bar charts usually have categories on the horizontal axis. • The bars are not usually equal widths. The bars in a bar chart are always equal widths. • Frequency density is plotted on the vertical axis. Bar charts have frequency plotted on the vertical axis. • Histograms are drawn when the data is continuous like an ordinary graph and the data can be put into classes (e.g. 100 ≤ h < 200). • The area of a bar represents the frequency. Drawing a histogram To draw a histogram, we need to ϐirst convert the frequencies to frequency densities because in a histogram it is the area of the bar rather than its height which represents the frequency.