Complications, sometimes serious, have been reported following STARR, but the procedure is now considered safe and effective. STARR is contraindicated in patients with weak sphincters (fecal incontinence and urgency are a possible complication) and with anismus (paradoxical contraction of the pelvic floor during attempted defecation). The operation has been shown to improve rectal sensitivity and decrease rectal volume, the reason thought to create urgency. 90% of patients do not report urgency 12 months after the operation. The anal sphincter may also be stretched during the operation. STARR was compared with biofeedback and found to be more effective at reducing symptoms and improving quality of life.