There are a number of ways of representing data diagrammatically.

Scatter Graphs

These are used to compare two sets of data. One set of data is put on the x-axis (the horizontal axis) and the other on the y-axis (the vertical axis). If one set of data depends upon the other, this is put on the y-axis (and is known as the 'dependent variable'). For example, if you were plotting a child's height at various times, the height would depend upon the time and so the height is the dependent variable and goes on the y-axis, whereas time doesn't depend on anything and so is the independent variable and goes on the x-axis. Usually, we are looking to see if there is a relationship between the two sets of data. We draw a line of best fit. This should have roughly the same number of points above and below it. The less scatter there is about the best-fit line, the stronger the relationship is between the two quantities. If the points are close to the best-fit line, we say that there is a strong correlation. If the points are loosely scattered, there is a weak correlation. We say there is zero correlation if there is no linear relationship between the variables- in other words if we can't draw a meaningful best fit line. Also, if the best fit line slopes upwards, like it does below, then the things we are comparing go up together. We say that there is a positive correlation. If the line slopes down, the 'dependent variable' decreases as the 'independent variable' increases. We say there is a negative correlation.

Bar Chart

A bar chart is a chart where the height of bars represents the frequency. The data is 'discrete' (discontinuous- unlike histograms where the data is continuous). The bars should be separated by small gaps.

Pie Chart

A pie chart is a circle which is divided into a number of parts.

The pie chart above shows the TV viewing figures for the following TV programmes:
Eastenders, 15 million

Casualty, 10 million

Peak Practice, 5 million

The Bill, 8 million

Total number of viewers for the four programmes is 38 million. To work out the angle that 'Eastenders' will have in the pie chart, we divide 15 by 38 and multiply by 360 (degrees). This is 142 degrees. So 142 degrees of the circle represents Eastenders. Similarly, 95 degrees of the circle is Casualty, 47 degrees is Peak Practice and the remaining 76 degrees is The Bill.