Probability and the chi-squared test

Probability is hugely important in a wide variety of different areas, including finance, insurance, product testing and weather forecasting. It is also vital in scientific research. If a new drug is being tested in a drug trial and the conditions of some of the participants improve but those of others don’t, how do we know if this is due to chance or the effect of the drug? Maths expert Dan Foulder explains

Statistical tests allow us to determine whether the probability of correlations, or differences between sets of results, are due to chance or if they are significant. In A-level and AS biology you may encounter three different statistical tests: the chi-squared test, Student’s t-test and correlation coefficient. In this Vital statistics we look at probability in genetic crosses and the chi-squared test.

Probabilities are usually expressed as decimals. If something is certain to happen, it has a probability of 1. If something is certain not to happen, it has a probability of 0.