Contrary to the number of books at home, the number of ebooks did not contribute to students’ academic language comprehension

Number of books at home as an indicator of socioeconomic status: Examining its extensions and their incremental validity for academic achievement. Birgit Heppt, Melanie Olczyk & Anna Volodina. Social Psychology of Education, Jun 17 2022. https://rd.springer.com/article/10.1007/s11218-022-09704-8

Abstract: The present study investigates the incremental validity of the traditional books-at-home measure and selected extensions (i.e., number of children’s books and number of ebooks) for explaining students’ academic achievement as measured by their academic language comprehension. Using multiple linear regressions, we additionally explore the role of the source of information (i.e., whether information is given by parents or children). Based on cross-sectional data of a German sample of 2353 elementary school children from Grades 2 through 4, we found that parents’ information on the number of books and children’s books contributed to students’ academic language comprehension over and above parental occupation and education. Children’s information on the number of books did not further increase the amount of explained variance, and the effects were smaller than those for parents’ information. Yet, when investigated separately, both parents’ and children’s information on the number of books and children’s books at home predicted students’ academic language comprehension and mediated the relationship between more distal structural features of socioeconomic status (i.e., parents’ occupational status and education) and the outcome variable. No effect emerged for the number of ebooks. Our findings point to the robustness of the traditional books-at-home measure when used in parent questionnaires.

Discussion

The current study investigated the incremental validity of the books-at-home measure beyond other commonly used SES indicators (i.e., parents’ occupational status and education) in explaining academic language comprehension. In particular, we examined whether selected extensions of the traditional books-at-home measure, namely, the number of children’s books and the number of ebooks, increase the validity of the books-at-home measure and whether the predictive value of the number of books and the number of children’s books differs by information source (i.e., whether parents or children answered the question). Additional analyses examined whether the number of books and children’s books as indicated by both parents and children mediated the relation between more distal structural SES features and students’ academic language comprehension.

Predictive validity of the books-at-home measure and its extensions

We found that parents’ information on the number of books and children’s books at home significantly increased the amount of explained variance in students’ academic language comprehension, even when considering parental education and occupational status (HISEI). The number of ebooks, however, did not contribute to the explanation of students’ academic language comprehension. A similar pattern of results emerged when using children’s information instead of parents’ information. Thus, children’s estimates, which were only assessed for the number of books and the number of their own books but not for the number of ebooks, contributed significantly to the explanation of their academic language comprehension. Moreover, parents’ books and children’s books, both when assessed by parents and by children, mediated the relationship between parents’ occupational status and education as well as students’ academic language comprehension. When simultaneously considering parents’ and children’s estimates of the number of books at home, however, only parents’ information on the number of books and the number of children’s books remained significant. The results thus show that children’s information on the number of books at home is of limited predictive value compared to parents’ information for explaining student achievement (see Table S5 in the Supplemental Material for additional findings in support of this interpretation). Overall, the findings indicate that when used in the parent questionnaire, the validity of the traditional books-at-home measure is not compromised by the greater availability of ebooks and can be slightly increased by additionally considering the number of children’s books at home.

The present study’s results corroborate previous findings that confirm the interrelatedness of different SES indicators while underlining their distinctiveness (e.g., Bukodi & Goldthorpe, 2013). Thus, although the different measures for assessing a family’s SES showed substantial amounts of shared variance, parental occupation status (HISEI), parental education, number of books, and number of children’s books all contributed independently to the explanation of student achievement. This suggests that they capture slightly different aspects of SES and cannot be used interchangeably. Simultaneously, the present study adds to the literature by examining the importance of the number of children’s books and the number of ebooks as well as the role of the respondent (parents vs. children) in increasing the predictive value of the traditional books-at-home measure. Furthermore, mediation analyses’ results confirmed and extended prior research that pointed to the mediating role of combined indices of the number of books and children’s books for the relation between different SES measures and students’ academic achievement (e.g., McElvany et al., 2009; McMullin et al., 2020; Myrberg & Rosén, 2009). The present findings thus further support the assumption that parents’ occupational status and education should be conceived of as distal structural features of SES whose impact on students’ learning outcomes can at least partly be explained by more proximal process-oriented features such as the learning stimulation tied to books and children’s books available at home (cf. Gustafsson et al., 2011; McElvany et al., 2009).

In terms of underlying mechanisms, which help to explain the relation between the number of books at home and student academic achievement, theoretical considerations suggest that the number of children’s books may be a better proxy for learning stimulation and joint reading activities than the number of parents’ books and, thus, may be an even more valid indicator of students’ cultural capital and learning resources. However, remarkably, this measure is not typically considered in large-scale assessments (with the exception of TIMSS and PIRLS), and its individual effects in predicting student achievement (i.e., net of the number of parents’ books) are usually not investigated. Hence, whereas prior research mostly used combined measures of the number of parents’ and children’s books and found that they were positively related to, for instance, students’ reading comprehension (Gustafsson et al., 2011; McElvany et al., 2009), we established the number of children’s books as an independent predictor of students’ academic language comprehension.

For the number of ebooks, the present findings challenge the assumption that the process of digitalization and the greater availability of digital devices threaten the validity of the traditional books-at-home measure (cf. Schwippert, 2019). In line with prior studies on media use (Kinder-Medien-Studie, 2018; Statista, 2021) that did not report widespread use of ebooks, the vast majority of parents in our study indicated owning 0 to 10 ebooks or chose not to answer the question. We suspect that this very uneven distribution and resulting variance restriction, which differed sharply from all the other books-at-home indicators (Fig. S1 in the Supplemental Material), is the driving force for explaining the null effects in the present study (for convergent findings, see Pagel, 2016). Potential differences in the use of ebooks and printed books in joint interactions among parents and children (cf. Krcmar & Cingel, 2014; Ross et al., 2016) might additionally have come into play.

The present study is among the very few to examine parents’ and children’s ratings of the number of books at home (e.g., Engzell, 2018; Jerrim & Micklewright, 2014) and, to the best of our knowledge, is the first to compare the predictive value of the number of books and the number of children’s books for these different information sources. In line with the studies by Engzell (2018) and Jerrim and Micklewright (2014), for instance, we found exceptionally low agreement between parents’ and children’s information on parents’ books and children’s books. Although it is not possible to determine which ratings are more accurate, we have reason to assume that elementary school children are the less reliable information source given their limited capacity for estimating amounts (Harel et al., 2007). Additionally, considering the stronger relations between parents’ estimates and students’ academic achievement compared to students’ estimates, our findings support the inclusion of the books-at-home measure in the parent questionnaire rather than in the student questionnaire (see Hovestadt & Schneider, 2021, for convergent findings regarding parental education).

Limitations, future directions, and conclusion

Several limitations exist in the current study. First, no information was available on the processes that occur within families, which might help to explain the effects of the number of books and the number of children’s books on students’ learning outcomes. While it can reasonably be assumed that books at home form an important basis for home literacy activities, such as joint reading activities or talking about reading experiences (e.g., Martin & Mullis, 2013; McElvany et al., 2009), future studies should deliberately assess students’ home literacy activities to inform our understanding of the role of parents’ books compared to children’s books for student outcomes.

Second, the present analyses are based on cross-sectional data and, thus, do not allow for drawing causal inferences. We assumed and modeled the various SES indicators as predictors of students’ academic language comprehension and can reasonably exclude reverse causality for most relations. Parents’ number of books and, in particular, their occupational status and education are most likely unaffected by their children’s academic language comprehension. However, reciprocal relations may occur between academic language comprehension and children’s own books, as children with greater mastery of the academic register may demand and be supplied with more books than students who are less proficient in academic language comprehension (cf. Mol & Bus, 2011).

Third, students’ academic language comprehension was the only outcome measure involved in our analyses. Academic language proficiency has been shown to be substantially related to competencies in a variety of domains, such as reading comprehension, mathematics, and science (e.g., Schuth et al., 2017; Volodina et al., 2021b), thus confirming it as a meaningful variable for investigating social inequalities in student achievement. However, the predictive value of the books-at-home measure and its extensions might be smaller for less language-bound measures.

Fourth, although we controlled for parents’ occupational status and education, which are both substantially related to the various books-at-home measures and students’ academic language comprehension, further measures that might help capture an even more nuanced picture of the relation between the number of books at home and student achievement were not considered. Specifically, information on parents’ home ownership, living space, and recent or upcoming moves, which all may relate to the number of books at home were not included in the dataset. In particular, frequent relocations may pair with a diminished personal book stock independent of a person’s occupational status and education.

Despite these limitations and open questions, which are subject to future research, the present study’s results may serve as an important basis for selecting and assessing SES indicators in social research. In particular, they increase our knowledge of the validity of the books-at-home measure, which is ubiquitously used in surveys and large-scale assessments but the quality of which has only rarely been scrutinized.