Results from the Camberwell Cohort study indicated that for adults diagnosed with intellectual disabilities in early life, the (a) majority of symptoms disappeared by adolescence. (b) original diagnosis had been changed by middle age. (c) overall quality of their lives was lower than that of non-impaired peers. (d) level of impact on their lives was unrelated to the severity of the disability

(c) overall quality of their lives was lower than that of non-impaired peers.

Explanation:

Camberwell Cohort which simply means group of English individuals with intellectual disabilities who participated in a long-term study.

Therefore, in a Camberwell Cohort study prepared by Julie Beadle‐Brown, Glynis Murphy, and Michele DiTerlizzi, which was published in 2009 concluded that, even though, it was difficult to reach conclusion, the study helps in affirming some support for the popularly held belief that Quality of Life is lower for those with intellectual disability and for those with challenging behaviour, compared to those who do not have intellectual disabilities

Hence, the right answer is: overall quality of their lives was lower than that of non-impaired peers.