Bibliometric analysis of the literature on phonological awareness in bilingual children

Purpose: to characterize the profile of scientific production in the international literature on phonological awareness in bilingual children between 2011 and 2020. Methods: a bibliometric analysis was made with the search for articles in ERIC, LILACS, MEDLINE, and SciELO databases, using descriptors in English. The articles were selected based on the eligibility criteria, by reading the titles, then reading the abstracts, and lastly, reading the full-text articles. Results: a total of 1,167 articles were analyzed, 1,152 of which were excluded for not meeting the inclusion criteria. Hence, 15 articles were selected for full-text reading and bibliometric analysis. The United States was the country with most publications, followed by Brazil, Singapore, and China. The approach of the studies was predominantly quantitative, followed by qualitative; the most common type of study was cross-sectional, with samples of more than 100 participants. Conclusion: there was a greater number of publications in the last 3 years, most of them cross-sectional ones, presenting better phonological awareness performance among bilinguals, with positive results in reading.


INTRODUCTION
Bilingualism, though still a widely debated term, is a global phenomenon. It identifies people who are fluent in at least two languages, capable of efficiently producing and understanding both of them 1 . New languages can be acquired in two ways. The first one is the early acquisition, when the person learns the second language (L2) between birth and childhood. This is further classified into simultaneous (when two languages are acquired at the same time) or sequential (when L2 is learned after the first language [L1] has been fully acquired). There are also the late bilinguals, who acquire L2 in adolescence or adulthood 2,3 . The demand for bilingual education has increased over the years, due to the increasingly dynamic and globalized world. Hence, parents have chosen to provide bilingual education to their children, so they will be prepared to live in such a world and experience other cultures 4,5 . Moreover, using L2 to learn regular school subjects further helps acquire that language 6,7 .
The literature is not yet unanimous on the best method to teach L2, as there are various acceptable bilingual teaching plans 8 . However, studies state that bilingual education must be based on a well-planned program, with the following characteristics: teaching to read and write in the mother tongue, and afterward developing these skills in L2; teaching school subjects in L1, without translating them, thus providing the basis for the comprehension of L2; and teaching and helping students master L2 in quality well-developed classes 9 .
Students must understand the rules of the alphabetic principle of writing (i.e., the links between phonemes and graphemes) to learn to read and write, both in L1 and L2. In its turn, understanding this principle requires the phonological awareness skill 10 .
Phonological awareness is the ability to segment a sequence of letters into sound units (phonemes) and manipulate them 11 . This skill is used to associate graphemes to phonemes and understand that such units are present in different words 10-12 . Thus, providing bilingual education to children while they are learning to read and write may positively influence their cognitive development, including attention, working memory, executive functions, and reading skills [13][14][15] .
Concerning phonological awareness, bilingual children can learn phonological aspects faster than monolingual ones, according to the cross-language transfer theory 16 . Phonological awareness transfer from L1 to L2 and vice-versa demonstrates that when bilingual children have this skill stimulated in one language, it will probably be transferred to the other one, as well 17 .
An eight-article integrative review showed that six of them revealed benefits in the phonological awareness of bilingual children in comparison with monolingual children. The bilingual children performed better in phonological awareness than their monolingual peers. Thus, L2 may positively influence the development of phonological awareness 18 . Therefore, the following research question was established for this study: "What is the profile of the scientific production in the Brazilian and international literature addressing the role of phonological awareness in bilingualism?". Bibliometrics is a quantitative analysis method for scientific studies and it can be used, in this case, as a methodology to measure the scientific production and contribution regarding the present topic 19,20 .
Hence, the objective of this bibliometric review is to characterize the profile of the Brazilian and international scientific production on phonological awareness in bilingual children.

METHODS
This is a bibliometric review of the state-of-theart research on the role of phonological awareness in bilingualism. Bibliometrics quantitatively analyzes information to organize, characterize, and classify publications retrieved via search mechanisms, making it possible to identify patterns and the state-of-the-art in a given field 21 . Articles published in the last 10 years (between January 2011 and April 2020) were searched in Brazilian and international journals in ERIC, LILACS, SciELO, and MEDLINE databases. The said period was established to search for publications because the topic in question was still incipient in the first decade of the 2000s. Moreover, this research aims to gather recent information in order to meet its objective of outlining the profile of the scientific production on bilingualism.
The following descriptors regarding the topic were used, with the free terms and the Boolean operators in English: bilingualism AND phonology, bilingualism AND phonological awareness, and bilingualism AND phonological skills.

Eligibility Criteria
The eligibility criteria to select the sample were as follows: a) articles published in Brazilian and international journals in full text and available in the database; b) in English; c) experimental, observational, and review articles published in English in the last 10 years. Opinion articles, case series, case studies, communications, and articles approaching bilingualism for deaf people were not included.
The articles were selected by reading their title, then reading their abstract, and lastly reading the full text of articles potentially relevant to the review. Duplicate articles were excluded and the variables of interest regarding the selected articles were extracted and tabulated in a spreadsheet, with the following data: year of publication, journal name, country of publication, research design, keywords, the journals' impact factor, Qualis, and main indexing, objectives, and results ( Figure 1). The descriptive analysis of the results was made based on frequency distribution, with their absolute (n) and relative (%) numbers.

LITERATURE REVIEW
A total of 1,167 articles published between January 2011 and April 2020 were found. Of these, 1,152 were excluded for not meeting the eligibility criteria. Such a high number of studies were due to a restricted descriptor selection -especially regarding the population of interest of the research, as there could be comparative studies between children and adults. Nonetheless, considering that this is still an incipient topic, it was decided to read the articles in full text to outline this criterion. Another hypothesis for this expressive initial number is the significant quantity of publications with the isolated descriptors that were chosen. Hence, the filters and Boolean operator combinations were essential to select the articles -which The 2019 studies focused on investigating the participants' performance in phonological awareness skills, especially comparing different groups. One study 23 investigated the phonological awareness competence in bilinguals at different levels. Another one 24 sought to understand the roles of phonological skills in people whose L1 was Chinese and L2, English. On the same perspective of these articles, researchers 25 compared Chinese-English bilinguals with English monolinguals regarding phonological awareness and other linguistic skills.
The recent studies [23][24][25][26][27][28][29] followed the same method- As for countries, the United States had the most publications in the period, with 26.66% (four articles), while Brazil, Singapore, and China had 13.33% (two articles) each. The other countries had only one published study each ( Figure 3). The publications were predominantly in English, while 13.33% (two articles) were in both Brazilian Portuguese and English. Hence, the United States is noticeably leading the publication of research on bilingualism, in comparison with the number of studies published on the topic in other countries. This is especially due to the reality in many regions of the country, where there are children of Latin-American background 30 , a large number of immigrants, and the emerging need for understanding how these children develop phonological awareness to learn to read and write.

Figure 3. Number of publications per country
A total of 61 different keywords were found, of which multilingualism 27,28,31 , phonological awareness [22][23][24]26,29,32,33 , and bilingualism 22,25,27,30,33 were the most frequent ones (Figure 4). Keywords are tools for database indexing, which makes them an important source of access to scientific articles. They enable the researcher to obtain information on the content of a text beyond what has been presented by the title and abstract 34,35 . However, the variety of descriptors found in this research and the lack of homogeneity in concordant keywords may reflect the difficulty in finding publications in the databases. The Reading and Writing and International Journal of Bilingual Education and Bilingualism were the only two of the 12 journals with more than one publication -they had three and two, respectively ( Figure  5). The International Journal of Bilingual Education and Bilingualism 25,30 is a new journal, focused on topics such as bilingualism, multilingualism, bilingual education, and new language acquisition. The most cited one, Reading and Writing 29,35,36 , is an open-access interdisciplinary and interprofessional academic journal that explores aspects of literacy in institutional, sociocultural, and disciplinary contexts. The topics of the articles published in this journal encompassed comparisons between monolingual and bilingual children regarding metalinguistic awareness in writing 29 and the relationship of phonological awareness with learning to read and write 35 and with reading decoding 36 . The bilingual subjects performed better in only one study 29 , whereas the other ones did not show significant differences 35,36 . Quantitative studies were the most recurrent type (93.33%, corresponding to 14 articles); only one article (6.66%) had a qualitative approach. This one was an integrative review that addressed issues of bilingualism in childhood and adulthood and literacy 27 . Cross-sectional studies were the most frequent ones, totaling 12 (80%). Most of these compared participants in different groups regarding phonological awareness skills, collecting new data (Table 1). Regarding the sample, most studies had more than 100 participants. Cross-sectional studies, which are characteristically low-cost, can outline the profile of the studied population. In this bibliometric review, all of them had a comparative profile and demonstrated that bilingual children who are learning to read and write performed better in phonological awareness in reading in this group of children [23][24][25]30,33,36 , as already identified in previous studies 16,17 .
Two out of the 15 articles reviewed were longitudinal. The first one focused on testing over the years, in Cantonese-English bilingual children, the prosodic transfer hypothesis and the segmental phonological awareness transfer hypothesis, both alone and in combination, in the three latent variable structural equation models 26 . For the segmental transfer model, the sensitivity to Cantonese intonation helped the segmental phonological awareness in that language, which longitudinally contributed to the segmental phonological awareness in L2 (English) and, as a result, to reading words in English. Generally, the study results support a unified phonological transfer model, emphasizing the role of prosody in reading words in English among Cantonese-English bilingual children 26 .
The objective of the second longitudinal study 33 was to examine whether there were different growth patterns in the basic reading skills between Turkish-German bilingual and German monolingual students. It also investigated whether a common reading model would equally fit both groups. The study revealed that both groups congruently developed their reading comprehension and other reading-related skills (phonological awareness and decoding). The authors also highlighted that the bilingual children in the sample had a slightly higher phonological awareness, though their development was similar to that of the monolingual group.
Lastly, the studies varied in terms of language transparency, phonological awareness performance, exposure time, and relationship with reading development. Table 2 shows the variety of results regarding phonological awareness between bilinguals and monolinguals, as there is yet no consensus on the advantages and disadvantages of bilingual education [22][23][24][25][26][27][28][29][30][31][32][33][34]37 . To explore whether Zulu-English bilinguals have better results in phonological awareness, word reading, and reading comprehension tasks than their English monolingual peers.

Phonological awareness skills of English as Second Language (ESL)
learners: the case of first-grade Filipino Bilinguals 23 To compare the performance of full and partial bilinguals in phonological awareness tasks.
The bilinguals proficient in L1 and L2 performed better in phonological awareness than the bilinguals more proficient in L1.
Bidirectional cross-linguistic association of phonological skills and reading comprehension: evidence from Hong Kong Chinese-English bilingual readers 24 To investigate how phonological skills in L1 and L2 contribute to reading in both languages.
The study demonstrated the bidirectional association (from L1 to L2 and from L2 to L1) for reading comprehension -i.e., the knowledge of phonological aspects of Chinese contributed to reading comprehension in English, and the knowledge of phonological aspects of English contributed to reading comprehension in Chinese. Simultaneous acquisition of English and Chinese impacts children's reliance on vocabulary, morphological and phonological awareness for reading in English 25 To explore the role of bilingualism in the acquisition of reading, comparing bilingual with monolingual children.
There was no difference in the performance of bilinguals and monolinguals -except for the isolated word reading task, in which the bilinguals were superior.
Tone matters for Cantonese-English bilingual children's English word reading development: a unified model of phonological transfer 26 To investigate whether there is a phonological transfer from L1 to L2 in Cantonese-English bilingual children.
The study demonstrated the presence of phonological transfer between L1 and L2.

Study Title
Objective Results of the phonological awareness performance A comparative study on phonological acquisition and performance in phonological awareness by children exposed to a bilingual or monolingual family environment 28 To verify and compare the phonological acquisition and performance in phonological awareness tasks between children exposed to a bilingual home environment and children exposed to a monolingual home environment. The children exposed to a bilingual home environment got fewer answers right in the phonological awareness tasks, although no statistically significant difference was found.
Metalinguistic contribution to writing competence: a study of monolingual children in China and bilingual children in Singapore 29 To investigate how the components of metalinguistic awareness contribute to reading comprehension in bilingual and monolingual children.
The bilinguals performed better in phonological awareness than the monolinguals.
The effects of Spanish heritage language literacy on English reading for Spanish-English bilingual children in the US 30 To investigate the impact of bilingualism on children's literacy.
The bilinguals performed better in phonological awareness skills than their monolingual peers.

Profile of phonological awareness in bilingual and monolingual children 31
To compare the performance of phonological awareness skills in bilingual and monolingual students.
There was a differentiated performance in phonological awareness skills between the tested groups; the bilinguals had better results than the monolinguals. Bilingual children had greater mastery over the phonemic awareness skill, which is an integral and more complex part of phonological awareness. The relationship between phonological awareness and executive attention in Chinese-English bilingual children 32 To examine the relationship between phonological awareness and executive attention in bilingual children who are learning to read.
Bidirectional association between phonological awareness and the executive attention in the bilinguals.
Differential growth patterns in emerging reading skills of Turkish-German Bilingual and German Monolingual primary school students 33 To compare the basic reading skills in bilingual and monolingual children.
Both groups similarly developed phonological awareness.
Do bilingual children possess better phonological awareness? Investigation of Korean monolingual and Korean-English bilingual children 36 To investigate whether bilingual children have an advantage in phonological awareness skills.
The study results indicated that the bilingual children had an advantage over the monolinguals regarding phonological awareness.
Second-language learners' advantage in metalinguistic awareness: A question of languages' characteristics 37 To investigate phonological, morphological, and syntactic awareness skills in children who are learning L2.
There were no significant differences between the bilinguals and monolinguals concerning phonological awareness.
Genetic and environmental overlap between Chinese and English reading-related skills in Chinese children 38 To analyze the genetic and environmental influences on visual word recognition, receptive vocabulary, phonological awareness, phonological memory, and speech discrimination in L1 and L2 in twins.
The genetic factors play an important role in the phonological awareness of bilinguals, whereas the shared environmental factors contributed more to the Chinese phonological awareness. Moreover, learning to read in L2 did not interfere with the acquisition of L1.
Note: The review article 27 was not included in this table.
The journals with the highest impact factors were the Psychonomic Bulletin and Review 27 and Developmental Psychology 38 . This factor -which can be low, high, or non-impact -measures the quality of the journals and assesses the authors and researchers according to their publications and citations 39 . The journals listed as "not applicable" in the impact factor column of the table either did not have it or did not inform it on its website or in Scopus. The same applies to Qualis and indexing. Concerning the limitations of the study, despite its bibliometric design, new studies should focus on the descriptive approach of phonological awareness and its influence on written language development in bilingual children. There is also the emerging relevance of systematic review studies with meta-analyses, which can help understand phonological awareness strategies to favor the development of reading and writing in this population.