= Sequential probability ratio test
{title2=$S_t=\sum_{s=1}^t\log[f_1(Y_s)/f_0(Y_s)]$}
A <sequential probability ratio test> accumulates the <log-likelihood ratio> for two specified simple <statistical hypotheses> until it reaches an upper or lower boundary. An upper crossing favors the alternative, a lower crossing favors the null, and observations continue between them. Error-calibrated boundaries are approximately $\log[(1-\beta)/\alpha]$ and $\log[\beta/(1-\alpha)]$; discrete overshoot means these approximations need calibration.
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