A 2011 AHRQ review of the evidence of the effectiveness of CI in people with bilateral hearing loss — the device's primary use — found low to moderate quality data that showed speech perception in noisy conditions was much better for people who had implants in both ears done at the same time compared to people who had only one. The data also showed that no conclusions could be drawn about changes in speech perception in quiet conditions and health-related quality-of-life. There was only one good study comparing implanting implants in both ears at the same time to implanting them sequentially; this study found that in the sequential approach, the second implantation made no change, or made things worse.