6.8 The Alpha Threshold

While the previous section implies that low p-values are likely to lead to rejection of the null hypothesis, it does not say how low those p-values would need to be.  This decision is set by the researcher, and the cutoff value is often referred to as “alpha.” 

In most statistics textbooks and online tutorials that you encounter, alpha will be set to 0.05.  However, there is no statistical law mandating this.  As you perform and assess statistical tests, bear in mind always that the alpha threshold is ultimately an arbitrary cutoff. 

For a statistical test involving life-and-death consequences, an alpha threshold of 0.05 might not be appropriate; in such instances, a researcher would opt for a much lower alpha value, wanting to be more certain that results were not attributable to random chance.