In conclusion, this study has established psychometric
properties of the NEO-FFI in Icelandic. Although some identified
problems of other translations were also observed here, overall
the performance of the Icelandic NEO-FFI supports its use as a personality
trait measure in both general population and addiction
samples. In terms of using the NEO-FFI dimensions as phenotypes
within genetic studies, we concur with the authors of the NEO-FFI
(McCrae & Costa, 2004) that personality traits may extend to certain
overlaps of the five factors measured by the NEO-FFI or even
be characterized to the level of individual items. Thus, success at
finding genotype/phenotype associations may require not only
large sample sizes using current trait definitions, but also re-defining
which combinations of trait scores, or even which individual
item scores, represent personality traits with biological underpinnings
that can further our understanding of brain functions
shaping personality