The digit ratio (2D:4D) represents the proportion between the lengths of the second and fourth fingers and is influenced by prenatal androgen exposure. Amniocentesis studies show it negatively correlates with prenatal testosterone and positively with estrogen, meaning higher testosterone exposure leads to a lower (more masculine) digit ratio (). The interest in the relationship between digit ratio and human development has led researchers to explore its possible link with academic performance, a key indicator of educational success and learning progress (). Academic achievement, usually measured through grade point average (GPA) () or standardized tests (), is a multidimensional construct influenced by various factors (). Academic achievement may hypothetically be related to digit ratio via its connection with cognitive functioning ().
This hypothesis draws on the theory, which suggests that high fetal testosterone may inhibit left hemisphere development —affecting language— but enhance right hemisphere abilities such as spatial reasoning and mathematics. However, empirical evidence is inconsistent: studies and reviews report mixed findings on the relationship between digit ratio and cognition (), and noted the difficulty of establishing firm conclusions, calling for further research.
Therefore, the present systematic review and meta-analysis aim to critically examine and integrate current evidence on the relationship between digit ratio and academic performance.
In contrast to biological determinism, educational research emphasizes that performance depends primarily on modifiable factors —such as teaching quality, learning opportunities, and socio-cultural context (). From a constructivist and sociocultural perspective, and highlight that learning develops through environmental interaction and social mediation. Thus, it is crucial to move beyond deterministic interpretations and promote education as a transformative, inclusive, and evidence-based process grounded in equity. Given these inconsistencies, systematic reviews are valuable for synthesizing existing evidence on this potential link. To date, no such comprehensive analysis has been conducted.
This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (). The review has been registered in https://osf.io/nqj6y/?view_only=9543d438c7734fecb20f9926857b7672.
A systematic search was conducted in four electronic databases (MEDLINE/PubMed, Scopus, PsycInfo, and Cinahl) covering the period from their inception to July 25, 2024. Additionally, an updated search was performed in January 2025 to ensure the inclusion of the most recent studies. The following search terms, Boolean operators, and combinations were used: "Second-to-fourth digit ratio" AND "academic performance”, "Second-to-fourth digit ratio" AND academic achievement”, "Second-to-fourth digit ratio" AND “school”, “2D:4D ratio” AND "academic performance", “2D:4D ratio” AND academic achievement”, “2D:4D ratio” AND “school”, “digit ratio” AND "academic performance", “digit ratio” AND “academic achievement”, “digit ratio” AND “school”, “finger length” AND “academic performance”, “finger length” AND “academic achievement” and “finger length” AND “school”.
The investigations included in the review were limited to journal publications. The methodology was restricted to quantitative studies, with no additional methodological limitations applied. No exclusion criteria were based on age or gender. Only studies that addressed academic performance as a measure applied in exams or standardized tests were selected. Unpublished studies, theses, and dissertations were excluded.
Initial screening of titles and abstracts was conducted by one author to assess study eligibility. Subsequently, two authors independently reviewed the selected articles for inclusion. Discrepancies were resolved by consensus, and in cases of uncertainty, a third author was consulted. Reference lists and Google Scholar citations of included studies were also examined to identify additional relevant publications.
A standardized data extraction table was developed to facilitate the systematic collection and organization of relevant information. Data were manually extracted and synthesized. For each included study, information was recorded on the country of origin, sample characteristics (including sample size, mean age, and gender), digit ratio (2D:4D) measurements, academic performance indicators, and key findings.
The methodological quality of the included cross-sectional studies was evaluated using the Joanna Briggs Institute (JBI) Critical Appraisal Checklist for Analytical Cross-Sectional Studies (). Two reviewers independently performed the evaluations, resolving discrepancies through discussion and consensus. Each checklist item was rated from 0 to 2, and a total quality score was expressed as a percentage of the maximum possible score. Studies were classified as high (≥70%), medium (40–69%), or low quality (<40%) based on established thresholds ().
Pearson’s and Spearman’s rank correlation coefficients were used as effect size metrics to examine the association between digit ratio and academic performance. Meta-analysis was conducted using Meta-Essentials Workbooks (version 1.5) in Excel (), testing whether a significant correlation existed (effect size > 0, p < 0.05). A random-effects model was applied due to heterogeneity across studies, quantified using I² (), and prediction intervals estimating the consistency of effects. Subgroup analyses by hand side and sex were performed, along with sensitivity and leave-one-out analyses to detect outliers. Publication bias was evaluated using a funnel plot and Egger test; no asymmetry was assumed if the intercept was not significantly different from zero (p > 0.05). A 'trim and fill' analysis was also conducted to account for potentially missing studies.
From the initial set of 2,848 records, 7 were selected for full-text evaluation, and 5 studies were chosen for review. After conducting a citation search, 6 additional records meeting the inclusion criteria were identified, resulting in a total of 11 investigations included in the analysis (Fig. 1).
The total sample size across all investigations was 2971 participants, with the smallest and largest samples comprising 48 () and 814 () individuals, respectively. One study included only male participants (). Participant characteristics varied significantly, with ages ranging from 6 to 29 years. Only one study focused on school-age children (), two studies included secondary school students (; ), and the remaining studies involved university students (; ; ; ; ; ; ; ). Additionally, three studies restricted their samples to Caucasian participants (; ; ). Supplementary Table S1 shows the main characteristics of the analyzed investigations.
Six investigations used the Conventional Digit Ratio procedure (; ; ; ; ; ), while three studies carried out the Anatomical Digit Ratio (; ; ). Both types of measurements were administered in two investigations (; ). Among the eleven studies reviewed, most reported digit ratio measurements for both hands (; ; ; ; ), while some also included averages or inter-hand differences (; ; ). Only three studies assessed the right hand exclusively (; ; ). Measurements were generally taken with a caliper, except in and , who used a ruler, and , who relied on hand photographs.
The combined results showed significant differences between right- and left-hand digit ratios (right: 0.970 ± 0.017; left: 0.976 ± 0.013; p < 0.001), though the absolute difference was minimal (0.006, less than 0.4 mm). Likewise, sex differences were statistically significant for both hands (males: 0.970 ± 0.012 and 0.971 ± 0.012; females: 0.979 ± 0.017 and 0.982 ± 0.012; p < 0.001), but the effect size was very small, corresponding to an average finger length difference of only 0.6 mm.
Academic performance was primarily assessed through exam scores or grades from specifically selected subjects (; ; ; ; ; ; ). Three studies, however, used results from national tests: utilized scores from the Numeracy and Literacy sections of the National Standardized Assessment Tests, gathered grades from the medical school admission test along with the average exam scores, and used scores from The Senior Secondary School Board Examination.
The only study with primary school students found a weak, negative association between the conventional digit ratio and the difference between Numeracy and Literacy scores (r = -0.22; p = 0.03). No relationship was observed between the separate Numeracy and Literacy scores and the digit ratio for the entire sample (), with sex-based analysis showing mixed results.
Two studies reported mixed results on the relationship between digit ratio and academic performance in secondary school students. found positive associations between performance in mathematics and Anatomical R2D:4D (r = 0.22, p < 0.001) and Anatomical L2D:4D (r = 0.16, p < 0.005) in females. In contrast, found no significant relationships between final scores in Mathematics, English, and Biology and any of the Anatomical Digit Ratio measures.
Eight studies focused on university students, yielding mixed results., , , and found weak significant associations between academic performance and digit ratio for the entire sample. In contrast, , , , and reported mixed results, with weak correlations depending on gender or the academic performance measurement used.
Pooled data from eight studies (n = 2,150) indicated no correlation between the digit ratio of the right hand and academic performance [R = 0.023 (95% CI: -0.028 to 0.075)]. Heterogeneity was low (I² = 0.88%). Similar findings were reported for the left hand, with pooled data from six studies (n = 2,031) showing no correlation [R = 0.025 (95% CI: -0.079 to 0.028)] while heterogeneity was also low (I² = 0%). There were no differences between hands in this absence of correlation (p=0.151) (Figure 2).
The results by sex are shown in Figures 3 and 4. Pooled data from seven studies (n=1,267) indicated no correlation between the right-hand digit ratio and academic performance in females [R = 0.067 (95% CI: -0.04 to 0.174)]. Similarly, pooling data from seven studies (n=1,004) revealed no correlation in males [R = 0.051 (95% CI: -0.026 to 0.128)].
Heterogeneity was higher in females (I² = 57.8%) compared to males (I² = 0%), with no significant differences between the two subgroups (p = 0.787). For the left hand, there was also no correlation. Pooled data from five studies in females (n=1,183) showed [R = 0.05 (95% CI: -0.133 to 0.142); I² = 64%], and five studies in males (n=937) showed [R = 0.033 (95% CI: -0.052 to 0.017); I² = 0%]. No significant differences were found between the two subgroups (p = 0.652).
No evidence of publication bias was detected in studies assessing each hand separately [Egger: -0.04 (95% CI: -0.12; 0.05); p=0.34; Trim and fill imputed studies=0] (Figure 5).
The robustness of the meta-analysis results was demonstrated by the absence of outliers that could have influenced the findings, as confirmed by the leave-one-out method (Supplemental Table S2). Additionally, the results remained consistent when a sensitivity analysis using a fixed-effects model was performed, yielding an R of 0.019 (95% CI: -0.03 to 0.068).
The methodological quality was considered high quality in three studies (and medium quality in the remaining studies. A full description of the quality analysis was also provided in Table 1.
[i] 1. Were the criteria for inclusion in the sample clearly defined?; 2. Were the study subjects and the setting described in detail?; 3. Was the exposure measured in a valid and reliable way?; 4. Were objective, standard criteria used for measurement of the condition?; 5. Were confounding factors identified?; 6. Were strategies to deal with confounding factors stated?; 7. Were the outcomes measured in a valid and reliable way?; 8. Was appropriate statistical analysis used?
This systematic review sought to determine whether the digit ratio can serve as a useful indicator of academic performance. The analysis included a substantial number of studies with medium to high methodological quality, allowing comparisons between right and left hands and an evaluation of sex differences. While statistically significant differences between the two hands were found in both sexes, their magnitude was minimal, a finding consistent with , who also reported very small differences between hands using different assessment methods. Similarly, although sex differences in digit ratio were statistically significant, they were minor, supporting prior evidence that males generally have slightly lower 2D:4D ratios than females, possibly due to sex-based variations in bone length and finger soft tissue composition ().
The main finding of this research is that, although individual studies occasionally reported weak and inconsistent associations between digit ratio and academic performance in specific subgroups, the pooled results from the meta-analyses revealed no significant correlation between these two variables. This challenges long-standing theories suggesting that higher prenatal testosterone exposure influences brain development and directly impacts intelligence and learning (). Therefore, the evidence does not support the idea that digit ratio has a meaningful or predictive relationship with academic performance.
Results from previous studies have been highly contradictory. Some research found associations between digit ratio and specific cognitive domains such as verbal and numerical intelligence (; ), while others proposed that a lower digit ratio could reflect differences in brain organization among gifted children compared to standard groups (). However, other investigations did not support these findings. For example, found no significant correlation between digit ratios of either hand and verbal performance, arithmetic, comprehension, or intelligence quotient in a sample comprising both healthy children and children with ADHD. Similarly, reported no consistent associations between digit ratio and spatial or mental rotation abilities, and in some cases, the direction of the observed relationships was opposite to what was hypothesized.
The current review also confirmed that the lack of association between digit ratio and academic performance persisted regardless of the hand measured or the sex of participants. Concerning hand differences, recommended that future research should assess both hands, as outcomes can vary. Supporting this notion, observed that the left-hand digit ratio, but not the right, significantly predicted performance in numerical tasks among both men and women. Similarly, found that gifted boys had significantly lower left-hand ratios than their standard counterparts. Regarding sex, the literature remains inconsistent. For example, noted that some studies reported negative correlations between digit ratio and numerical performance across both sexes, whereas others observed such relationships only among women. Comparable inconsistencies were found in relation to verbal skills, preventing the identification of a clear pattern.
Several contextual and methodological factors must be considered when interpreting these findings. Academic achievement is known to be strongly influenced by numerous variables such as socioeconomic status and parental education (), previous academic performance (), and levels of physical activity (), yet few of the reviewed studies adequately controlled for these confounders. Age also appears to play a role, as the correlation between cognitive and biological factors tends to weaken with increasing age (). Moreover, most of the included studies were conducted on university students, with only one study focusing on children, limiting the generalizability of the conclusions.
Measurement techniques for digit ratio constitute another major source of variability. As effect sizes for 2D:4D are typically moderate to low (), precision in measurement is crucial. Digit ratio can be assessed through direct physical measurement or indirect methods, such as photocopies or digital scans. recommend direct measurements for smaller samples, where accuracy can be ensured, and indirect methods for larger samples requiring faster data collection. However, when direct and indirect measurements are combined within the same analysis —as occurred in the present meta-analyses— results must be interpreted with caution, since mixed methods can introduce error and bias (). Additionally, most reviewed studies did not employ computer-assisted techniques for measuring digit ratios, even though this approach is considered the most accurate and reliable compared to manual, photocopy, or scan-based methods (). highlighted several methodological limitations that are often overlooked in digit ratio research. Many studies focus excessively on identifying statistically significant correlations without considering the small effect sizes involved. For instance, differences in finger length below 1 millimeter are generally insignificant and lack clinical or practical meaning. Furthermore, issues such as multiple testing and selective reporting may further compromise the validity and reproducibility of reported findings.
In summary, the results of this systematic review clearly indicate that there is no meaningful association between digit ratio and academic performance, regardless of sex or the hand examined. By demonstrating that neither sex nor biological traits determine academic performance, this research reinforces the importance of designing inclusive educational strategies grounded in diversity and equity, thereby promoting the elimination of gender- or biology-related biases and prejudices in teaching. These findings further highlight the need to prioritize truly modifiable educational variables, such as teaching quality, active learning strategies, and equity (), while cautioning against deterministic or pseudoscientific interpretations of learning processes. Consistent with Piaget’s () constructivist and Vygotsky’s () sociocultural frameworks, genuine educational innovation should be based on pedagogical and social interventions that emphasize interaction, mediation, and environmental influences on cognitive development.
This review represents the first comprehensive attempt to synthesize evidence on the link between digit ratio and academic performance. Its main strengths lie in its novelty, the methodological rigor of its included studies, and the robustness of the meta-analytic results, which showed low imprecision, low heterogeneity, and satisfactory certainty of evidence. Nonetheless, several limitations should be acknowledged: most studies were conducted with university populations; potential confounding factors affecting academic performance were not always controlled; and the combination of direct and indirect measurement methods may have influenced reliability. Finally, language restrictions and the exclusion of gray literature may have further limited the scope and comprehensiveness of the review.
Preliminary scientific evidence suggests a lack of association between digit ratio and academic performance, irrespective of sex or the hand assessed. Further research focused on children and adjusting findings for potential confounding variables is necessary to ascertain whether a direct link between digit ratio, intelligence, and academic skills exists.
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