title:
        Educational Attainment and Cognitive Profile Heterogeneity: Evidence for Domain-Specific Performance Patterns in Large-Scale Cognitive Assessment

aims:
        1. To develop and validate a robust measure of cognitive profile heterogeneity using percentile-based relative performance indices within demographic strata, and examine whether individuals with higher educational attainment exhibit greater cognitive profile heterogeneity compared to those with lower educational attainment.
        2. To investigate whether the relationship between educational attainment and cognitive profile heterogeneity varies systematically across age groups, testing whether this association strengthens in older cohorts who have had extended exposure to specialized educational and occupational environments.

hypothesis:
        Primary Hypothesis: Individuals with higher educational attainment will demonstrate significantly greater cognitive profile heterogeneity, defined as larger discrepancies between their highest and lowest domain-specific percentile rankings within age-matched normative groups, compared to individuals with lower educational attainment.
        Secondary Hypothesis: The association between educational attainment and cognitive profile heterogeneity will be significantly stronger among older adults (ages 50+) compared to younger adults (ages 18-39), reflecting potential cumulative differentiation effects over extended periods of specialized engagement.

experimental_approach:
        experiment 1 - cognitive profile heterogeneity measurement: calculate domain-specific percentile rankings for each participant using the provided normative data within the available age bins ([18-29], [30-39], [40-49], [50-59], [60-69], [70-99]) to avoid age-education confounding. define cognitive profile heterogeneity as the percentile range (90th percentile domain minus 10th percentile domain) and interquartile range across domains for each individual. focus analysis on battery 26 (nâ318,300) which provides comprehensive domain coverage across 11 subtests spanning memory, reasoning, attention, and processing speed. validate the measure by demonstrating independence from overall performance level (grand index) and examining consistency across different subtest versions where available within the dataset.
        experiment 2 - educational attainment analysis: implement ordinal logistic regression treating education levels as ordered categories rather than continuous variables, with cognitive profile heterogeneity quartiles as the outcome variable. include age (continuous), gender, country, and time-of-day as covariates while accounting for the nested data structure using mixed-effects modeling with participants nested within testing sessions. apply bonferroni correction for multiple testing across different heterogeneity metrics and conduct sensitivity analyses excluding participants with incomplete batteries.
        experiment 3 - age-stratified analysis: conduct separate analyses within distinct age strata using the available age bins ([18-29], [30-39], [40-49], [50-59], [60-69], [70-99]) to avoid cohort confounding while examining whether education-heterogeneity associations vary across the lifespan. test for effect size differences across age groups using confidence interval comparisons rather than interaction terms to avoid assumptions about linear age effects. include comprehensive sensitivity analyses examining different age groupings and heterogeneity operationalizations.

importance:
        Current cognitive research emphasizes general cognitive ability or absolute performance levels, with limited understanding of how educational experiences relate to the development of heterogeneous cognitive profiles characterized by relative strengths and weaknesses across domains. While expertise research demonstrates domain-specific advantages, there lacks empirical investigation of whether educational attainment systematically relates to the development of differentiated cognitive profiles within the general population. This study addresses this gap by examining cognitive profile heterogeneity using percentile-based measures that capture relative performance patterns across cognitive domains, providing novel insights into how educational experiences may relate to the architectural differentiation of cognitive abilities without requiring problematic variance-based metrics or causal assumptions.
        
potential_impact:
        This research would advance individual differences theory by providing the first large-scale empirical evidence for systematic relationships between educational experiences and cognitive profile differentiation in the general population. The findings would extend Carroll's (1993) three-stratum theory of cognitive abilities by demonstrating that cognitive architecture may become increasingly differentiated with educational specialization, challenging assumptions about fixed cognitive structure. The percentile-based approach offers a methodologically sound alternative to problematic variance-based specialization metrics, potentially influencing future psychometric research on individual differences. For educational psychology, demonstrating education-related cognitive profile heterogeneity would support Ackerman's (1996) PPIK theory linking personality, interests, intelligence, and knowledge, while informing debates about educational tracking and specialization timing. The age-stratified findings would contribute to lifespan developmental theories by testing whether cognitive differentiation represents a developmental process extending beyond traditional developmental periods (Baltes et al., 2006). Practically, the research could inform educational assessment by shifting focus from general ability to profile analysis, supporting personalized learning approaches and career guidance based on relative cognitive strengths rather than overall performance levels.