A new sequential sampling scheme is proposed in which, after an initial batch sample, sampling is continued in batches of data-dependent sizes (at most k such batches), and then one-at-a-time with a data-dependent stopping rule. This new scheme requires about the same sample size as the fully sequential Anscombe-Chow-Robbins (ACR) sampling scheme but substantially fewer sampling operations. The problem of constructing fixed-width confidence intervals for the mean of a normal population with unknown variance is used as an illustration.
"Improving the fully sequential sampling scheme of Anscombe-Chow-Robbins." Ann. Statist. 25 (5) 2164 - 2171, October 1997. https://doi.org/10.1214/aos/1069362392