Factors that can increase the risk of heart disease are identified by epidemiological studies involving large numbers of people. Individual cases do not provide convincing evidence for or against a link.

Studies compare large amounts of data between groups that are matched in as many factors as possible.

You need to be able to evaluate the design for a study to test whether or not a factor is linked to a health problem, by commenting on sample size and how well the samples are matched.

Check that you can use data to develop an argument that a factor does or does not increase the chance of an outcome. Make sure that you know what a positive correlation would look like on a scatter graph.

Be able to identify the presence (or absence) of a scientific explanation as important for the acceptance (or rejection) of a claimed link causing a health problem.

The 'peer review' process is where other scientists who are experts in that field of science evaluate new scientific claims by studying the methods and results.

New scientific claims that have not yet been evaluated by the scientific community are less reliable than well-established ones.

A scientific claim may be questioned if other scientists have not replicated the results.