Evils of categorisation. Another e.g.

[kornbrot]

This is a really lovely example of  ++++ of regression & - - - - of categorisation!

Best

Diana

Differences in the 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line
Lukáš Kratochvíl 1 and Jaroslav Flegr 2
1 Department of Ecology, Faculty of Science, Charles University in Prague, Vinièná 7, 128 44 Praha 2, Czech Republic
2 Department of Philosophy and History of Science, Faculty of Science, Charles University in Prague, Vinièná 7, 128 44 Praha 2, Czech Republic
Abstract
Ratios often lead to biased conclusions concerning the actual relationships between examined traits and comparisons of the relative size of traits among groups. Therefore, the use of ratios has been abandoned in most comparative studies. However, ratios such as body mass index and waist-to-hip ratio are widely used in evolutionary biology and medicine. One such, the ratio of the 2nd to the 4th finger (2D : 4D), has been the subject of much recent interest in both humans and animals. Most studies agree that 2D : 4D is sexually dimorphic. In men, the 2nd digit tends to be shorter than the 4th, while in women the 2nd digit tends to be of the same size or slightly longer than the 4th. Nevertheless, here we demonstrate that the sexes do not greatly differ in the scaling between the 2nd and 4th digit. Sexual differences in 2D : 4D are mainly caused by the shift along the common allometric line with non-zero intercept, which means 2D : 4D necessarily decreases with increasing finger length, and the fact that men have longer fingers than women. We conclude that previously published results on the 2D : 4D ratio are biased by its covariation with finger length. We strongly recommend regression-based approaches for comparisons of hand shape among different groups.

Source: The Royal Society
http://rsbl.royalsocietypublishing.org/content/early/2009/06/22/rsbl.2009.0346.abstract?papetoc

Comment:
That was my favourite method for detecting transvestites, or at least it was...now I'll just have to go back to relying on beard length...

Posted by
Robert Karl Stonjek

------ End of Forwarded Message

Professor Diana Kornbrot
email:  d.e.ko...@herts.ac.uk    
web:    http://web.mac.com/kornbrot/iweb/KornbrotHome.html
Work
School of Psychology
 University of Hertfordshire
 College Lane, Hatfield, Hertfordshire AL10 9AB, UK
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[Doug Altman]

the conclusions of this study seem highly questionable!

At 20:10 25/06/2009, kornbrot wrote:

This is a really lovely example of  ++++ of regression & - - - - of categorisation!

Best

Diana

Differences in the 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line

Lukáš Kratochvíl 1 and Jaroslav Flegr 2

1 Department of Ecology, Faculty of Science, Charles University in Prague, Vinièná 7, 128 44 Praha 2, Czech Republic

2 Department of Philosophy and History of Science, Faculty of Science, Charles University in Prague, Vinièná 7, 128 44 Praha 2, Czech Republic

Abstract

Ratios often lead to biased conclusions concerning the actual relationships between examined traits and comparisons of the relative size of traits among groups. Therefore, the use of ratios has been abandoned in most comparative studies. However, ratios such as body mass index and waist-to-hip ratio are widely used in evolutionary biology and medicine. One such, the ratio of the 2nd to the 4th finger (2D : 4D), has been the subject of much recent interest in both humans and animals. Most studies agree that 2D : 4D is sexually dimorphic. In men, the 2nd digit tends to be shorter than the 4th, while in women the 2nd digit tends to be of the same size or slightly longer than the 4th. Nevertheless, here we demonstrate that the sexes do not greatly differ in the scaling between the 2nd and 4th digit. Sexual differences in 2D : 4D are mainly caused by the shift along the common allometric line with non-zero intercept, which means 2D : 4D necessarily decreases with increasing finger length, and the fact that men have longer fingers than women. We conclude that previously published results on the 2D : 4D ratio are biased by its covariation with finger length. We strongly recommend regression-based approaches for comparisons of hand shape among different groups.

Source: The Royal Society

http://rsbl.royalsocietypublishing.org/content/early/2009/06/22/rsbl.2009.0346.abstract?papetoc

Comment:

That was my favourite method for detecting transvestites, or at least it was...now I'll just have to go back to relying on beard length...

Posted by

Robert Karl Stonjek

------ End of Forwarded Message

Professor Diana Kornbrot
email:  d.e.ko...@herts.ac.uk   

web:    http://web.mac.com/kornbrot/iweb/KornbrotHome.html
Work
School of Psychology
 University of Hertfordshire
 College Lane, Hatfield, Hertfordshire AL10 9AB, UK
 voice:   +44 (0) 170 728 4626
   fax:     +44 (0) 170 728 5073
Home
 19 Elmhurst Avenue
 London N2 0LT, UK
    voice:   +44 (0) 208 883  3657
    mobile: +44 (0) 796 890 2102
   fax:      +44 (0) 870 706 4997

_____________________________________________________

Doug Altman
Professor of Statistics in Medicine
Centre for Statistics in Medicine
University of Oxford
Wolfson College Annexe
Linton Road
Oxford OX2 6UD

email:  doug....@csm.ox.ac.uk
Tel:    01865 284400 (direct line 01865 284401)
Fax:    01865 284424
www:     http://www.csm-oxford.org.uk/

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