When a result is statistically significant, it means it’s unlikely to have occurred by chance alone. For example, studies have found that people who smoke are more likely to die from lung cancer, and this result is statistically significant—meaning the link is unlikely to be random.
Statistical significance is usually assessed using a p-value. If the p-value is less than 0.05, it means there’s less than a 5% probability that the result is due to chance, and the result is considered statistically significant. A p-value greater than 0.05 is typically considered not statistically significant.
Significance can also be assessed using a confidence interval (CI), especially with risk ratios or odds ratios. If the 95% confidence interval includes 1.00, the result is not significant. For example:
- But if the 95% CI were (1.01–1.35), it would be significant, because the entire range is above 1.
- An odds ratio of 1.25 with a 95% CI of (0.99–1.33) is not significant.