The mismeasure of hands?

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Science  07 Jun 2019:
Vol. 364, Issue 6444, pp. 923-925
DOI: 10.1126/science.364.6444.923

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  • Some Questions About the Replicability and Practical Applications of Digit Ratio (2D:4D) Research
    • Gareth Richards, Teaching Fellow, School of Psychology, Newcastle University

    Leslie (1) makes clear that the 2D:4D literature is characterised by inconsistent findings and replication failures. The problem is arguably worse: questions concerning validity remain (2), and the field does not yet agree on what is the best measure of the ratio. As well as right hand and left hand 2D:4D, the average of these is sometimes used, as is directional asymmetry (i.e. the right-left difference) (3, 4). Studies typically use more than one predictor and report subgroup analyses, yet rarely correct for alpha inflation. To illustrate this problem: if right hand and left hand 2D:4D are examined in relation to just one outcome in males and females separately, there is a 20% chance of observing a spurious effect (i.e. Type 1 error) at p < 0.05. This issue is of course magnified when studies assess multiple outcome variables.

    Additionally, a fundamental question must be asked: what should be considered a successful replication in this field? For instance, if one study reports a correlation with right hand 2D:4D then another observes a similar correlation for the left hand, should the latter be considered a replication of the former? If yes, then an unrealistic picture of consistency may be painted. A related issue is how to interpret null-findings alongside significant effects. For example, a frequently cited study (5) reported a correlation between right hand 2D:4D and the testosterone/estradiol ratio in amniotic fluid; no such effect was observed fo...

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    Competing Interests: None declared.