Full context:   A 1996 behavioural genetics study of twins suggested that heritability (the degree of variation in a trait within a population that is due to genetic variation in that population) and environmental factors both influence all five factors to the same degree. Among four twin studies examined in 2003, the mean percentage for heritability was calculated for each personality and it was concluded that heritability influenced the five factors broadly. The self-report measures were as follows: openness to experience was estimated to have a 57% genetic influence, extraversion 54%, conscientiousness 49%, neuroticism 48%, and agreeableness 42%.