2.1. Sample and Procedure
Data were drawn from the longitudinal talent-study (e.g.,
Lavrijsen et al. 2021). This study was initiated in 2017 and followed a large community sample of 3409 early adolescents from 166 classes in 27 Flemish schools (49.6% boys, M
age = 12.41 years, age range 8.85–14.33 years, SD
age = 0.49) across secondary education. Schools were recruited for the study via open calls for participation within school networks. Among participating schools, all students who had successfully completed primary school (known as the A-stream) were invited to participate. This study was approved by the institutional ethical committee, and consent for participation was obtained from adolescents, parents, and teachers. Students had a slightly more advantaged social background than the Flemish secondary education student population, with 21.2% of the sample receiving financial governmental support for low-income families (compared with 25.7% of the general population), 11.9% speaking a different language at home (16.9% of the general population), and 14.1% having a mother without a secondary school degree (18.0% of the general population).
This study consisted of six waves (Grade 7 (Fall and Spring), Grade 8 (Fall and Spring), Grade 11 (Fall), Grade 12 (Spring)). Initially, schools registered to participate in the first four waves; accordingly, all schools continued their participation throughout Grades 7 and 8 (i.e., NG7 = 27 and NG8 = 27). However, when the last two waves were added to the study, 10 schools decided not to further participate in Grade 11 (i.e., NG11 = 17) and an additional 6 decided not to participate in Grade 12 (i.e., NG12 = 11). In addition, a number of students left the participating schools over the course of secondary education. For these reasons, the number of participants was reduced over the course of this study (nG7 = 3.409; nG8 = 2.861; nG11 = 1.567; nG12 = 988). Dropout was significantly related to adolescents’ Need for Cognition, with small differences in average levels between those continuing their participation and those dropping out (i.e., the average initial Need for Cognition among those who participated in all waves equaled 3.17, whereas the average initial Need for Cognition among those dropping out in Grade 8 equaled 2.84 (d = −0.41), among those dropping out in Grade 11 2.96 (d = −0.26) and among those dropping out in Grade 12 3.17 (d = −0.00)). Further analyses showed that average initial Need for Cognition in Grade 7 was somewhat higher in schools that continued participation throughout this study (average value 3.05) compared to schools discontinuing their participation (average value 2.93, d = −0.13).
Finally, in Grade 7 (Fall), parents were asked to complete at home a survey capturing parental educational level, cognitive stimulation at home, and parental autonomy support. For 2.886 students (84.7%), at least one parent completed the survey.
2.2. Measures
All survey measures were rated on a Likert-scale ranging from 1 to 5, with the endpoints labeled “Does not apply to me” and “Fully applies to me”. The reliabilities of measures were compared with threshold values by
DeVellis (
1991), which suggests that alpha’s above 0.70 indicate good reliability for research purposes (with alpha = 0.65 to be the threshold for “minimal acceptability”).
Adolescents’ Need for Cognition was assessed in Grades 7 (Spring), 8 (Spring), 11 (Fall), and 12 (Spring). It was measured with a Dutch translation of the German 14-item Need for Cognition scale by
Preckel and Strobel (
2017), for which the psychometric properties and validity for use with children and adolescents are well documented (
Keller et al. 2016;
Preckel and Strobel 2017). In the present study, the measure demonstrated very high reliability (α
G7 = 0.92/α
G8 = 0.93/α
G11 = 0.92/α
G12 = 0.93)
1.
The Big Five personality traits were assessed in Grade 7 (Fall) and Grade 11 with the Quick Big Five (
Vermulst and Gerris 2005). Each of the five traits was assessed with 6 items. Overall, the reliabilities of each trait measure were good, with the exception of Openness in Grade 7, which was only minimally acceptable (Openness α
G7 = 0.68/α
G11 = 0.84; Conscientiousness α
G7 = 0.76/α
G11 = 0.80; Extraversion α
G7 = 0.84/α
G11 = 0.72; Agreeableness α
G7 = 0.89/α
G11 = 0.90; Neuroticism α
G7 = 0.87/α
G11 = 0.87).
Academic intrinsic motivation was assessed in Grade 7 (Fall) and Grade 11 with 4 items from the subscale of the Academic Self-Regulation Questionnaire by
Ryan and Connell (
1989). The subscale exhibited good internal consistency (α
G7 = 0.87/α
G11 = 0.86).
Parental educational level was surveyed in Grade 7 (Fall) by asking parents to report the highest qualification level achieved. This was coded as 0 = no secondary education; 1 = secondary education; 2 = Bachelor’s; and 3 = Master’s or beyond. As is common in research on social background (
Avvisati 2020), the highest educational level among both parents was used to indicate parental educational level.
Cognitive stimulation at home was measured in the parent questionnaire in Grade 7 (Fall) with 5 items from a scale by
Stevens et al. (
2014). These items assessed different forms of cognitive stimulation at home (i.e., buying or borrowing books for the child, watching documentaries together, discussing the news with the child, attending an exhibition together, discussing school). The internal consistency of the scale was minimally acceptable (α
G7 = 0.66). If both parents responded, their responses were averaged.
Parental autonomy support (e.g., I let my child plan his/her schoolwork himself/herself) was surveyed among parents in Grade 7 (Fall) with 4 items from the scale by
Cheung et al. (
2016). Internal consistency of the scale was good (α
G7 = 0.77). If both parents responded, their responses were averaged.
Finally, cognitive ability test was measured in Grade 7 (Fall) with a well-validated Flemish test (CoVaT-CHC) that assessed both fluid and crystallized intelligence (
Magez et al. 2015). An IQ-score for each adolescent was calculated based on a comparison of test results with a norming sample.
2.3. Analyses
First, we analyzed the rank-order stability of Need for Cognition, the Big Five personality traits, and academic intrinsic motivation between Grades 7 and 11. As random measurement error can affect stability estimations, we modeled Need for Cognition, the Big Five traits and academic intrinsic motivation as latent variables. Given the complexity of the measurement model (i.e., three different latent constructs measured at two time points, with Need for Cognition in particular indicated by a relatively high number of items), we decided to parcel items (i.e., we averaged subsets of items to indicate each construct). Indeed, it has been argued that such parceling alleviates a number of psychometric problems as compared to individual items, and it in particular improves modeling efficiency and stabilizes parameter estimates (
Matsunaga 2008). In our measurement model, each latent construct at each measurement point was thus indicated by three parcels (i.e., for Need for Cognition, parcels consisted of items 1–5, 6–10, and 11–14; for the Big Five traits, parcels consisted of items 1–2, 3–4, and 5–6; and for academic intrinsic motivation, parcels consisted of items 1–2, 3, and 4).
We first tested the invariance of this measurement model over time, that is, we tested whether model fit of the measurement model would be affected by imposing equality constraints for corresponding factor loadings and intercepts of these parcels between Grades 7 and 11 measurements (e.g., we imposed an equality between the factor loading of Need for Cognition on the first parcel in Grade 7 and the corresponding factor loading in Grade 11). In particular, we tested both metric invariance (i.e., invariance in the equality of factor loadings) and scalar invariance (i.e., invariance of factor intercepts). As χ2 is known to be highly sensitive to sample size (
Putnick and Bornstein 2016), we compared model fit of measurement models using three indicators of model fit, that is, the Comparative Fit Index (CFI), the Root Mean Square Error of Approximation (RMSEA), and the Standardized Root Mean Squared Residual (SRMR). As a rule of thumb, invariance then could be established when the decrease in CFI was not larger than 0.010 (
Cheung and Rensvold 2002), when increases in RMSEA were not larger than 0.010, and when increases in SRMR were not larger than 0.025, respectively (
Chen 2007).
After establishing measurement invariance, we then estimated latent intercorrelations between Need for Cognition, the Big Five traits, and academic intrinsic motivation between the Grade 7 and 11 assessments.
Second, to study longitudinal growth in Need for Cognition across adolescence, a series of univariate latent growth curve models were specified in which individual Need for Cognition levels in Grades 7, 8, 11 and 12 were explained by an intercept, a linear slope, and a quadratic slope term after establishing scalar measurement invariance over time for these measures. In the growth curve models, loadings were set to take unequal spacings between measurements into account (e.g., for the linear term, t = 0 for Grade 7, t = 1 for Grade 8, t = 4 for Grade 11, and t = 5 for Grade 12). For each variable, a model with only an intercept term was compared with a model with both an intercept and a linear term, and then to a model with an intercept, a linear, and a quadratic term. The Bayesian Information Criterion (BIC) was used to see which of these models yielded the best fit with the data (lower BIC values indicate better model fit).
Using the best fitting models from the previous step of the analysis, a series of latent class growth models (
Jung and Wickrama 2008) were specified to identify distinct classes in trajectories of Need for Cognition over time. Several criteria were used to decide on the optimal number of latent classes. First, BIC was evaluated between solutions with different classes. As BIC generally tends to decrease with each additional class, we considered at which number of classes the decrease in BIC elbowed. Second, the quality of the classification was addressed by estimating the entropy of the solution, which measures the accuracy of assigning individuals to trajectory classes. Third, the qualitative substantive value of each class was examined: when a solution with
k classes included two classes that exhibited only minor substantive differences in between, the more parsimonious
k − 1 class solution was preferred. Finally, solutions yielding very small classes (e.g., only 5% of the sample) were not preferred.
In a final set of analyses, class membership was related to cognitive ability, parental educational level, cognitive stimulation at home, and parental autonomy support. Class membership was predicted by using the three-step Bolck–Croon–Hagenaars (BCH) method (
Bolck et al. 2004). The BCH method yields for each individual and each class a weight, which reflects the assignment probability of the individual to that class. However, in this study, the BCG method sometimes yielded negative weights, which inhibited further estimations. Hence, instead of predicting weights, we decided to predict for each individual the most likely class (i.e., the class with the highest positive weight) by cognitive ability, parental educational level, cognitive stimulation at home, and parental autonomy support using a multinomial multivariate regression model.