R package Sequential. Sequential: Exact Sequential Analysis for Poisson and Binomial Data. Functions to calculate exact critical values, statistical power, expected time to signal and required sample sizes for performing exact sequential analysis. All these calculations can be done for either Poisson or binomial data, for continuous or group sequential analyses, and for different types of rejection boundaries. In case of group sequential analyses, the group sizes do not have to be specified in advance and the alpha spending can be arbitrarily settled.