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Comparing indirect methods of digit ratio (2D:4D) measurement
Christoph J Kemper1, Andreas Schwerdtfeger
1Department of Psychology, Johannes Gutenberg-University Mainz, Mainz, Germany. kemperc@uni-mainz.de
Summary
Computer software offers the most precise method for measuring finger length ratios (2D:4D), crucial for indexing prenatal androgen exposure. While slower, its superior reliability aids research, especially with limited data or small effect sizes.
Area of Science:
- Anthropometry
- Endocrinology
- Behavioral Science
Background:
- The 2D:4D digit ratio is a proposed biomarker for prenatal androgen exposure.
- Various indirect methods exist for measuring digit ratio, but their precision and efficiency are not well-established.
- Reliable measurement is critical for detecting subtle associations between digit ratio and other variables.
Purpose of the Study:
- To systematically compare the measurement precision and economy of different indirect methods for assessing digit ratio.
- To determine the most reliable method for future digit ratio research.
Main Methods:
- Three independent raters measured finger lengths of 60 participants using a plastic ruler, caliper, and computer software.
- Measurement precision was evaluated using intraclass correlation coefficient (ICC), technical error of measurement (TEM), and relative technical error of measurement (rTEM).
Main Results:
- All methods demonstrated acceptable measurement precision.
- Computer software yielded the highest precision estimates (excellent reliability).
- Caliper and ruler methods showed progressively lower precision, with the ruler being least precise.
- Software-based measurements were more time-consuming than manual methods.
Conclusions:
- Computer software is recommended for digit ratio research due to its superior reliability, particularly when effect sizes are small or sample sizes are limited.
- Advanced features of software (e.g., zooming, contrast adjustment) aid in accurate landmark identification.
- The enhanced reliability of software methods supports robust investigation of 2D:4D ratio associations.
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