4 Results
4.2 Does the claim of superior EF levels and poorer language levels hold
groups of bilingual learners?
The main analysis in article 1 displayed a large degree of heterogeneity within overall EF. To explore the heterogeneity, 11 moderator analyses were performed, both methodological ones (sample size, publication year and laboratory) and moderators representing sample characteristics when a bilingual advantage is theorized to occur (AoA, L2 proficiency, age, degree of balanced bilingualism, and SES level [equal levels across monolingual and bilingual learners]). Since it is impossible to randomly assign bilingualism, all studies in the meta-analysis were group comparison studies. Sample characteristics (non-verbal IQ and SES) representing uneven group comparisons in the primary studies were therefore also included as moderators in the analysis.
The only moderators significantly related to differences in overall EF outcomes were the moderators laboratory and SES level. The laboratory of York was identified as a laboratory driving up the effect sizes in favour of a bilingual advantage. Only bilingual children from the medium-SES class had a bilingual advantage, in contrast to children from the low- or medium- to high-SES classes.
Articles 2 and 3 compare the language levels of different groups of early bilingual learners with those of a monolingual control group. In total, 4 group comparisons of early bilingual and monolingual learners’
language levels were examined. In article 2, the bilingual toddlers’
language levels were compared to the levels of a monolingual control group. The analysis in Appendix 4 shows additional analysis of a subgroup of these bilingual toddlers compared to the monolingual
control group. This subgroup was composed by merging the subgroup of bilingual toddlers who had some L2 input at home with the subgroup exposed mainly to L2 at home. (Article 2 found the language levels of these two groups of early bilingual learners to be equal.) However, with no direct comparison to a monolingual control group, the analysis in article 2, research question 2, shows the difference in language levels between the early bilingual toddlers exposed mainly to L1 and the early bilingual toddlers with some or mainly L2 exposure at home. When the difference in language level between the bilingual toddlers with L2 exposure at home and the monolingual group is known, an indirect comparison of the bilingual toddlers exposed mainly to L1 at home and the monolingual learners can be made. The 4th comparison of early bilingual and monolingual learners’ levels of language is presented in article 3. The children were then 10 years old.
The results from article 2, the additional analysis in Appendix 4 and the results in article 3 all display differences that do not favour the early bilingual learners both in investigated age levels and almost all aspects of the pre-adolescents’ language skills. For pre-adolescents, the language levels were equal across language groups for one aspect only (d = 0.34, n.s.). The effect size differences for the other linguistic aspects favour monolingual learners (d= .78, d= .60, d = 0.74.). The difference in language levels between the early bilingual toddlers and their monolingual peers was d = 0.54 in favour of the monolingual learners.
The smallest difference in language levels identified in toddlerhood (d=
.39) was between the subgroup of bilingual toddlers who were exposed to some or mainly Norwegian input at home and the monolingual control group. Note, however, that the majority of these children might well have had a native majority language-speaking parent at home (see Table 1 in section 3.2.1). The language levels of the early bilingual toddlers exposed mainly to L1 at home were d= 0.56 lower than those of early bilingual toddlers with some L2 exposure at home; hence, this subgroup also had lower language levels than their monolingual peers. Table 1 in
section 3.2.1 indicates that this subpopulation of bilingual learners most likely did not have a native Norwegian-speaking parent at home, although considering the amount of missing data, it is difficult to draw such conclusions.
4.3 Does the claim of superior EF levels and poorer language levels hold across different cognitive domains and linguistic aspects?
The additional analysis presented in Appendix 4 and article 2 shows that the early bilingual learners had poorer language comprehension in toddlerhood. In the pre-adolescents, the early bilingual learners also exhibited poorer vocabulary levels (d = 0.74, p < 0.001), listening comprehension (d = 0.60, p = 0.002) and reading comprehension (d = 0.78, p = 0.009). Morphology skills could not be investigated in the preadolescents due to invariant test results. The pre-adolescent bilingual learners had text cohesion vocabulary skills equal to those of the monolingual learners (0.34 d, p = 0.102).
Regarding the EF domains, the moderator analysis showed that different EF domains significantly moderated the outcome of overall EF (F= 4.59, df = 23.2, P= 0.002). The results of monitoring (g = 0.24, 95% CI [0.058, 0.428]), switching (g = 0.329, 95% CI [0.192, 0.446]) and cold inhibition (g = 0.196, 95% CI [0.034, 0.358]) were in favour of bilinguals, in contrast to hot inhibition, inhibition of attention, attention, planning and working memory were the results were either similar for the monolingual and bilingual learners or unreliable. The Egger’s regression test showed a significant asymmetry for the domain of monitoring (β = 2.580, SE = 0.77, Z= 3.35, p = 0.001). Partialing out the small study effect with PET analysis showed that the effect sizes were then nonsignificant. For cold inhibition, a regression analysis of published versus unpublished studies showed a larger effect for published studies, in spite of a symmetric funnel plot. In fact, the mean effect of unpublished papers of cold
inhibition was in favour of monolinguals. Switching was not influenced by publication bias or the small study effect. Thus, switching was the only domain in which a bilingual advantage was detected after partialing out the small study effect or controlling for publication bias. An analyse of the mean effect size for the domain of switching showed a bilingual advantage of d = 0.27, but there was a large observed variation in effect sizes (ranging from -0.517 to 1.667).
The analysis of the relationship between task on overall mean at the domain level was either unreliable (switching and cold inhibition) or not significant (monitoring).
4.4 Is the predictive pattern of language and decoding skills to reading comprehension different for bilingual and monolingual learners?
The prediction of linguistic skills and decoding to reading comprehension was equal across groups, F (5.0) = 0.555, p = 0.734.
When controlling for all literacy variables, vocabulary did not predict reading comprehension (p = 0.872). Listening comprehension had the greatest impact on reading comprehension and explained 26.01% of the variance in reading comprehension, followed by text cohesion vocabulary, which explained 18.49% of the variance. Decoding skills explained only a marginal variation in the 5th graders’ reading comprehension (R= 0.009%).