Weaning and variability evaluation (WAVE) score, rapid shallow breathing index (RBSI) and clinical impression. These figures show how the risk/fold increase in risk of failing extubation associated with positive WAVE score (that is above 0.5) increases with increasing RSBI during SBT (above), or the clinical impression of the physician at the end of the SBT (below). The risk is defined as the number of patients who failed divided by the total number of patients in a given group (for example, above 0.5). The fold increase in risk is the risk divided by the average risk of failure of the dataset (approximately 12%). There are 396 patients with low RSBI (45 failed, 351 passed), and 26 patients with high RSBI (6 failed, 20 passed), while 12 passed had no RSBI reported. There is no statistically significant difference between the number of failed and passed that had no RSBI reported (P value = 0.2, chi-squared test for proportions). There are 330 patients with low/average risk of failure (32 failed, 298 passed), and 45 with high risk of failure (12 failed, 33 passed), while 7 failed and 52 passed have no perceived risk of failure reported. There is no statistically significant difference between the number of failed and passed that had no perceived risk of failure reported (P value = 0.98, chi-squared test for proportions).