Scattergraphs, or scatter diagrams, look at a possible correlations between two variables. Large amounts of data are usually recorded to investigate trends, and scattergraphs are particularly useful for analysing this kind of data.
Scattergraphs enable correlations between disease and lifestyle choices, and correlations between disease and environmental or industrial conditions, eg possible effects of pesticides and industrial chemicals, to be seen.
It is also a good way of looking at trends across different countries.
The scattergraph below uses data from a landmark scientific paper of 1975, where Ken Carroll investigated women eating different amounts of animal fat and deaths from breast cancer.
Each data point represents a piece of data from a different country.
The data shows a clear trend between animal fat intake and death rates from breast cancer.
If a scattergraph does show a correlation between two sets of data, you can add a line of best fit to illustrate the trend. This is a line that goes as close to as many points as possible.