What is statistical significance?

Statistical significance occurs when an observed pattern in the data is unlikely to have happened by chance (i.e. it falls outside of the range of values predicted by the null hypothesis).

Significance is usually denoted by a probability value (p-value). When this falls below a certain alpha value, then we say the result of the test is statistically significant. The alpha value is often set at 0.05 – that is, when there is a less than 5% probability that the result could have happened by chance.