Borderline Intellectual Functioning – Exploring the Invisible

Abstract

Borderline intellectual functioning (BIF) is poorly recognised phenomenon characterised by lower-than-average cognitive functioning (intelligence quotient [IQ] of 70–85) and challenges in adaptive behaviour. This thesis explored the individual, neurocognitive and societal aspects of BIF through a systematic literature review and two population-based studies. The findings were compared with parallel aspects of the general population (GP): people with average intelligence and learning problems (LPs), and people with mild intellectual disabilities (MIDs). In the systematic literature review, which applied pre-specified eligibility criteria, 1,726 abstracts and 203 full texts were evaluated; 49 studies were closely analysed. In the population-based studies, the highly unique Finland-in-Miniature sample, originally planned to evaluate people with intellectual disabilities, was used. The sample was gathered in 1962 from 57 municipalities (N = 416,973) and followed until 1998. For the purpose of this research, three groups were formed: BIF (IQ = 70–85; n = 416/156), MID (IQ < 70; n = 312/170) and LP (IQ > 85; n = 284/91). Results of the study show that people with BIF struggled more than their peers of average intelligence in cognitive and academic performance, social relations, education, work and mental health. Moreover, a 3.4-fold risk for severe mental health problems and a 2.7-fold risk for disability to work were found. An increased risk for social exclusion was also evident because of a combination of a high prevalence of mental health problems, non-secure work and low educational level. In general, BIF was in between the continuum from LP to MID, but had unique features of more mental health problems and insecure employment. It was concluded that people with BIF have evident, manifold risks for well-being throughout their lifespan; yet, they are not recognised in research or practice. To enable support, BIF needs to be acknowledged at every stage of the lifespan. Societal and political discussions and guidelines are needed. The volume of research concerning BIF should be increased; in particular, population-based studies are necessary, as are studies focusing on more individual perspectives, such as recognition and support.

Keywords: borderline intellectual functioning, cognitive difficulties, lifespan, mental health, social exclusion