We find that a futility boundary of l 1 =0 (which corresponds to a stop for futility if a negative trend is observed) leads in all considered scenarios to lower or equal average sample numbers (Table 2 ).
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We find that a futility boundary of l 1 =0 (which corresponds to a stop for futility if a negative trend is observed) leads in all considered scenarios to lower or equal average sample numbers (Table 2 ).