Alpha Value (α)
- α ("Alpha") is the probability of concluding that there is a difference between the groups studied, but in reality there is no difference (also known as making a "type I error").
- α is usually set a-priori to be 0.05.
- A finding is considered to be statistically significant if the p-value obtained is < 0.05.
- Simplistically, α is the chance of making a type I error.
- The smaller the α value the lower the risk of making a type I error. Note: doing this also usually means the investigator will need a larger sample size to a difference if it exists.
- The alpha value and sample size are the two most common contributors to the power of a study.
the alpha to be smaller (e.g., going from an α < 0.05 to an α < 0.025) prior to starting a study will make it harder
for investigators to find a difference if in fact a difference is to be
- However, if a difference is found when doing this, the risk of making a type I error is lower.
What is an Alpha Value (α)?