Let . A value such that is considered "significant" (i.e., is not simply due to chance) is known as an alpha value. The probability that a variate would assume a value greater than or equal to the observed value strictly by chance, , is known as a P-value.

Depending on the type of data and conventional practices of a given field of study, a variety of different alpha values may be used. One commonly used terminology takes as "not significant," , as "significant" (sometimes denoted *), and as "highly significant" (sometimes denoted **). Some authors use the term "almost significant" to refer to , although this practice is not recommended.