Borderline intellectual functioning is associated with poor social functioning, increased rates of psychiatric diagnosis and drug use--a cross sectional population based study.

Borderline intellectual functioning is defined by the DSM IV as an IQ range that is between one to two standard deviations below the mean (71<IQ<84), and a considerable percentage of the population is included in this definition (approximately 13.5%). The few studies performed on this group indicate that borderline intellectual functioning is associated with various mental disorders, problems in everyday functioning, social disability and poor academic or occupational achievement. Using data from the Israeli military, we retrieved the social and clinical characteristics of 76,962 adolescents with borderline intellectual functioning and compared their social functioning, psychiatric diagnoses and drug abuse with those of 96,580 adolescents with average IQ (± 0.25 SD from population mean). The results demonstrated that the borderline intellectual functioning group had higher rates of poor social functioning compared to the control group (OR=1.9, 95% CI=1.85-1.94). Individuals with borderline intellectual functioning were 2.37 times more likely to have a psychiatric diagnosis (95% CI=2.30-2.45) and 1.2 times more likely to use drugs (95% CI=1.07-0.35) than those with average IQ. These results suggest that adolescents with borderline intellectual functioning are more likely to suffer from psychiatric disorders, poor social functioning and drug abuse than those with average intelligence, and that borderline intellectual functioning is a marker of vulnerability to these poor outcomes.