A pseudocount is an amount (not generally an integer, despite its name) added to the number of observed cases in order to change the expected probability in a model of those data, when not known to be zero. It is so named because, roughly speaking, a pseudo-count of value α {\textstyle \scriptstyle {\alpha }} weighs into the posterior distribution similarly to each category having an additional count of α {\textstyle \scriptstyle {\alpha }} . If the frequency of each item i {\textstyle \scriptstyle {i}} is x i {\displaystyle \scriptstyle {x_{i}}} out of N {\textstyle \scriptstyle {N}} samples, the empirical probability of event i {\textstyle \scriptstyle {i}} is