Reviews and primary research focusing on group mean score differences between immigrant and native-born individuals on cognitive ability measures are based in Sweden and The Netherlands (see te Nijenhuis & van der Flier, 1999, for a review of Dutch studies). Early research in The Netherlands examining group score differences on cognitive ability tests within the context of selection demonstrated that length of time living in The Netherlands was positively correlated with scores on tests of verbal reasoning (r = 0.30) but not for nonverbal reasoning (van Leest & Bleichrodt, 1990). Additionally, on the General Aptitude Test Battery (GATB) vocabulary subtest, the non-immigrant majority group scored substantially higher than North African immigrants in The Netherlands (d = 2.07; te Nijenhuis & van der Flier, 1997). Te Nijenhuis and van der Flier (1999) identified a pattern where verbal-based cognitive ability tests tended to demonstrate score differences between immigrants and non-immigrants, but nonverbal tests did so to a much smaller extent overall, if at all. These studies, as well as those discussed below, imply that language proficiency may play a role in observed differences for natives compared to immigrants on some cognitive ability tests, especially tests with a high verbal load.
An additional review of studies examining cognitive ability test score differences of non-immigrants (ethnic Dutch) participants compared to immigrants (Turks, Moroccans, Surinamese, Netherlands Antilleans and Indonesians) reported that all but South-East Asian immigrants scored lower than the non-immigrant group (te Nijenhuis, de Jong, Evers & van der Flier, 2004). Indicating further evidence of potential language proficiency and acculturation effects, a comparison of first-generation immigrants to later generations found significant increases in cognitive ability scores. Te Nijenhuis and colleagues stated that ‘it is clear that for certain groups the average IQ scores or test scores are underestimates ofg due to low proficiency in the language of the test..(p. 426).
Te Nijenhuis, Willigers, Dragt and van der Flier (2016) recently analysed a very large database of cognitive ability test data from Dutch samples. They concluded that group mean differences in cognitive ability test scores can be largely explained by subtests within cognitive test batteries. Specifically, native Dutch-speakers consistently outperformed those whose native language was not Dutch on subtests that were considered language- loaded (i.e., tests that require proficiency in the language used in the test). This results in an underestimation of immigrants’ overall cognitive ability due to these verbally-loaded aspects of the test battery. Interestingly, te Nijenhuis and colleagues also found that, after taking language proficiency into account, there was little unaccounted variability that could be attributed to cultural bias. This may raise questions about the effect of cultural values and norms on group differences within these tests, but offers more clarity regarding the pattern that language proficiency may have on these differences.
Valentin Kvist and Gustafsson (2008) conducted a study in Sweden which demonstrated large group differences between immigrants and non-immigrants on crystallized intelligence and, to a smaller extent, on broad visual perception, with immigrants scoring lower than non-immigrants. In a follow-up study also conducted in Sweden, Valentin Kvist (2011) reported that European immigrants scored lower than native Swedes (approximate d = 2.0) while the difference was much larger for non-European immigrants (approximate d = 3.0). For visual perception, European (d = 0.75) and non-European immigrants (d = 1.50) scored lower than non-immigrant majority group. Furthermore, although the differences were less extreme, immigrants from European countries scored lower on measures of fluid intelligence (d = 0.22) as compared with non-immigrants. This finding is important as race is, to a degree, controlled in this comparison as the majority of the European immigrants were White. For non-European immigrants, the differences were larger (d = 0.62).
It is important to note the larger literature examining cross-national differences in cognitive ability test scores. As noted previously, much of this research has used samples of children. While these results may not fully generalize to working populations, the findings are nevertheless instructive. van de Vijver’s (1997) meta-analysis of crossnational mean score differences on cognitive ability tests found that the mean effect size was close to zero, but the distribution of effect sizes was positively skewed and the median value demonstrated differences between national cultures. The magnitude of the effect size was moderated by a number of factors and the level of stimulus complexity, with larger effect sizes for more complex stimuli. The type of task was related to the effect size such that Western tasks produced larger differences than tasks developed in the local culture. Finally, the level of national wealth was related to the magnitude of the effect sizes such that effect sizes were larger in comparisons involving wealthier countries.