A developmental psychologist hypothesized that children who are reared in families where more than one language is spoken will have higher abstract reasoning abilities as adolescents than children reared with just a single language spoken. After obtaining IRB approval through his university, he placed an ad in the local college newspaper asking for parent/child volunteers. Through responses to his ad he was able to recruit 40 children from 12 to 15 years of age, 20 from bilingual families and 20 from monolingual families.He then administered the Wechsler Intelligence Scale for Children (WISC) to all children and focused his analyses on a subscale that assessed abstract reasoning ability. He found that children from bilingual families scored on average 5 percentile points higher on the abstract reasoning subscale than children from monolingual families. This difference was statistically significant at the α=.05 level. What kind of research is this?