English: The x axis represents participants being recruited over time, while the y axis represents the total number of (desired) responses. The two shaded columns represent the points at which an analysis will be undertaken. If the number of responses is four or below after 18 participants, the trial will "stop for futility", also known as a no go decision. This will also happen if there are ten or fewer responses after 33 participants. If there are more than ten responses after 33 participants, there will be a go decision and the null hypothesis will be rejected. This means that there is evidence that the treatment works. This image was created in R, using the curtailment package.