Monday, September 26, 2016

Measuring the 2D:4D ratio

(Source: https://ibmathsresources.com/2013/05/05/finger-ratio-predicts-maths-ability/)

Measured mean values of 2D:4D ratios

Study of 464 university students (253 females) ages 18-22 in Duke University, North-Carolina, USA. 

Method: using NIH ImageJ software on digital scans.
  • men
    • right hand: 0.9594
    • left hand: 0.9503
  • women
    • right hand: 0.9722
    • left hand: 0.9650

Study on children of various ethnic backgrounds (798 children in the total sample: 90 Berbers, 438 Uygurs, 118 Han, and 152 Jamaicans). 

Method: photocopies.

  • Han (China - oriental): right hand 0.954
  • Berber (Morocco - caucasian): right hand 0.950
  • Uygurs (Morocco - caucasian): right hand 0.946
  • Jamaican (Afro-Caribbean): right hand 0.935
(source: "Sex and ethnic differences in 2 to 4 digit ratio of children", Manning, Stewart, Bundred, Trivers, in Early Human Development 80(2):161-8 · December 2004, retrieved July 1st 2016)

Study on 840 Nigerian Igbo and Yoruba adolescents (50% male). 

Method: caliper
Mean 2D:4D ratios:
  • female:
    • left: 0.95
    • right: 0.97
  • male:
    • left: 0.94
    • right: 0.96
(Gabriel, S. Oladipo, B. Fawehinmi Hakeem, I. Edibamode Ezon-Ebidor, A. Osunwoke Emeka, and S. Ordu Kenneth. "Second to fourth digit ratio in Nigerian Igbos and Yorubas." Scientific Research and Essays 4, no. 10 (2009): 1146-1148.)

Study on 83 adults 18-20 years old, 32 males and 51 females in Uttarakhand, India. 

Method: caliper. Mean 2D:4D ratios:

  • female:
    • left: 0.98
    • right: 0.99
  • male:
    • left: 0.967
    • right: 0.99
Broken down in left-handed and right handed participants:

We see above that
  • females have higher 2D:4D ratios (left and right) than men
  • the 2D:4D ratio is slightly lower on the dominant side (left-handed participants had a lower left 2D:4D than right 2D:4D, and right-handed participants a lower right 2D:4D than left 2D:4D)

("2D:4D Ratio in Adult Female and Their Comparison with Males: An Anthropometric Study from Northern India", Anamika Jaiswal, Ankit Kaushik, A K Singh, Government Medical College, Haldwani, Uttarakhand, India, Annals of Woman and Child Health, Vol. 3; Issue 4: 2017) 

Study on 419 Guatemalan women - very low 2D:4D for women

  • female:
    • left: 0.9337
    • right: 0.9322
"The digit ratios for our sample are lower than those typically found in the literature. For the right hand, mean 2D:4D is 0.9322 (with a standard deviation of 0.0315); for the left hand the mean is 0.9337 (with a standard deviation of 0.0321)."
(Aycinena, Diego, and Lucas Rentschler. "Discounting and digit ratio: Low 2D: 4D predicts patience for a sample of females." Frontiers in behavioral neuroscience 11 (2018): 257.)

2D:4D ratios in Malay, Chinese and Indian males and females (150 participants)




(source: Nayak, Satheesha B., Dhiviah Nair, Vimal Ravi, and Ashwini P. Aithal. "A comparative study on digit ratio and hand patterns of three ethnic races of Malaysia." Egyptian Journal of Forensic Sciences 8, no. 1 (2018): 56.)

Measurements were made directly using a scale.

Concerning the right hand:
  • males with a feminine (2D >= 4D) digit ratio:
    • Malay: 40% (32 + 8)
    • Chinese: 60% (16 + 44)
    • Indian: 52% (20 + 32)
  • females with a feminine digit ratio:
    • Malay: 52% (40 + 12)
    • Chinese: 36% (12 + 24)
    • Indian: 76% (16 + 60)

Concerning the left hand:
  • males with a feminine (2D >= 4D) digit ratio:
    • Malay: 60% (32 + 28)
    • Chinese: 44% (32 + 12)
    • Indian: 48% (36 + 12)
  • females with a feminine digit ratio:
    • Malay: 24% (20 + 4)
    • Chinese: 36% (24 + 12)
    • Indian: 35% (11 + 24)
(Nayak, Satheesha B., Dhiviah Nair, Vimal Ravi, and Ashwini P. Aithal. "A comparative study on digit ratio and hand patterns of three ethnic races of Malaysia." Egyptian Journal of Forensic Sciences 8, no. 1 (2018): 56.)


Study on 86 students in North-East Pakistan 

  • female:
    • left: 0.979
    • right: 0.977
  • male:
    • left: 0.958
    • right: 0.958
"Of the 86 students, 42 (49%) were male and 44(51%) were female, with a mean age of 19.55±1.017 and19.86±0.905 years, respectively. The mean 2D:4D ratio for males on the left hand was 0.958±0.029 and for females it was0.979±0.363 (p=0.004). The ratio for the right hand for males  was  0.958±0.031  and  for  the  females  it  was0.977±0.035 (p=0.011)"
(Khan, Muhammad Zirik, Muhammad Hammad Malik, Roshaan Ahmad, Huma Saeed Khan, Shahid Hasan, and Zeeshan Ashraf Chaudhry. "2D: 4D digit ratios in males and females and its correlation with simple reaction time: A cross sectional Study at Combined Military Hospital (CMH), Lahore, Pakistan." JPMA (2019).)

Study on 100 adults (56 males) from the northwest of India

  • female: 1.00
  • male: 0.97
"The mean 2D:4D ratios in males were observed to be 0.97 by direct method and 0.96 by scan method. In females the ratio was 1.00 and 0.99 by direct and scan methods respectively"
(Jain, Monica, Usha Dhall, Suryamani Pandey, and Satyendra Jain. "Second to Fourth Digit Ratio (2D: 4D) in North-West Indians: Sexual Dimorphism." Journal of Anatomical Society of India 61, no. 2 (2012): 242-245.)


Study on 350 South Indian adolescents. 

Method: direct measurement.
Mean 2D:4D values:
  • males: 0.95
  • females: 0.99

(Kanchan, Tanuj, G. Pradeep Kumar, Ritesh G. Menezes, Prateek Rastogi, PP Jagadish Rao, Anand Menon, B. Suresh Kumar Shetty et al. "Sexual dimorphism of the index to ring finger ratio in South Indian adolescents." Journal of forensic and legal medicine 17, no. 5 (2010): 243-246.)

Study on 60 Greek men and 60 Greek women (randomly selected, age range 19-25 years). 

Method: calliper.
  • female:
    • left: 1.001
    • right: 1.002
  • male:
    • left: 0.973
    • right: 0.974
(Kyriakidis, Ioannis, and Paraskevi Papaioannidou. "Epidemiologic study of the sexually dimorphic second to fourth digit ratio (2D: 4D) and other finger ratios in Greek population." Collegium antropologicum 32, no. 4 (2008): 1093-1098.)



Comparative evaluation of 2D:4D ratios in males and in females in different studies


Author
Population
n
Gender
2D:4D
Manning et al (1998)[10]
English
400
M
F
0.98
1.00
William et al (2000)[15]
American
108
146
M
F
0.96
0.97
Swami et al (2013)[16]
Harayani Brahmins
Kashmiris pandits
150
150
M
F
M
F
0.95
0.98
0.99
1.001
Present study
Tibeto-Nepalese
Indo-Nepalese
200
200
M
F
M
F
1.004
0.99
1.003
1.004

Abbreviations: 2D:4D, second to fourth digit ratio; F, female; M, male.

Study on 269 adolescents of 18–19 in South-East India. 

  • males and females: 0.97

Method: calliper.
"Mean 2D: 4D ratio of the study population was 0.97±0.082. There was no significant difference in mean 2D: 4D ratios (Males=Females) (...). "
(Jeevanandam, Saravanakumar, K. Muthu Prathibha, and K. Raman. "Relevance of 2D: 4D Ratio as a Marker of Depression in Adolescents of a South Indian Medical College-A Cross Sectional Study." International Journal of Physiology 7.2 (2019): 80-85.)


Study on 100 medical students in South-west-India

  • female:
    • left: 0.98
    • right: 0.97
  • male:
    • left: 0.98
    • right: 0.97
Hundred first year medical students (n=100) (males= 50 and females =50) of S. N. Medical college, Bagalkot.

Measurement method: digital calliper
"In Males, the ratio varied from 0.89 to 1.04 with mean and standard deviation of 0.97 ± 0.03 on right side and on left side it varied from 0.85 to 1.03 with mean ± SD of 0.98 ±0.04. While in females ratio varied from 0.91 to 1.11 with Mean ± SD of 0.97±0.04 on right side and on left side it varied from 0.83 to 1.12 and Mean ± SD of 0.98 ±0.04 on left side. (...) When all the cases below and equal to 0.97 were considered as males and those above 0.97 were considered as females, one could accurately determine the sex up to 90% accuracy."
(Sheelavant, Santosh, and Manjula Patil. "Role of 2nd Digit: 4th Digit Ratio (2D: 4D Ratio) in Establishing the Biological Profile of an Individual." Medico-Legal Update 19.2 (2019): 175-179.)

Study on 247 students (180 female, 67 male) of College of Health Technology, Ilese Ijebu, Ogun State, Nigeria

Method: calliper and hand scan
Results (mean 2D:4D):
  • males:
    • right hand: 0.95 (calliper), 0.94 (hand scan)
    • left hand: 0.96 (calliper), 0.94 (hand scan)
  • females:
    • right hand: 0.95 (calliper), 0.95 (hand scan)
    • left hand: 0.96 (calliper), 0.95 (hand scan)
 ("Digital Ratio and Academic Performances of College Students", T. Adenowo, and O. Oladokun.
International Journal of Recent Innovations in Medicine and Clinical Research 1 (1): 29-36 (August 2019))

Study on 100 subjects (50 male, 50 female) in North-Pakistan

Method: "compass" and ruler
Results (mean R2D:4D):
  • males: 0,991
  • females: 0,995
 ("THE GENDER DIFFERENCE OF 2nd TO 4th DIGIT LENGTH AND LENGTH RATIO (2D:4D) IN LOCAL POPULATION", Foundation University Med J 2014; 1(1):11-14, Syed Muarraf Hussain, Saadat Ali Khan, Syeda Maria Ali, SyedAbdul Mughees Hussain)


Study on the Bini people in South Nigeria

400  subjects  (225  males,  175  females), ages 18-60
"The  males  had  the  Left  Digit  Ratio  0.98±0.03,  Right  Digit Ratio 0.97±0.02. While in the females the Left Digit Ratio was 0.98±0.05, Right Digit Ratio 0.99±0.04."
(Paul, John N., Deborah A. Akinola, and Chibuike Obiandu. "A Descriptive Study of Gender Difference in Digit Ratio among Bini Ethnic Group of southern Nigeria.")


Germans have significantly higher mean 2D:4D than Chinese

"The German sample had significantly higher 2D:4D ratios than the Chinese sample but in both samples males had significantly lower 2D:4D ratios than females."
(Wernicke, J., Zabel, J. T., Zhang, Y., Becker, B., & Montag, C. (2020). Association between tendencies for attention-deficit/hyperactivity disorder (ADHD) and the 2D: 4D digit ratio: a cross-cultural replication in Germany and China. Early Human Development, 143, 104943.)


1,5 year old children in Japan

  • Males:
    • left: 0.909 ± 0.048
    • right: 0.938 ± 0.055
  • Females
    • left: 0.913 ± 0.049
    • right: 0.937 ± 0.049
(Yamada, Y., Ebara, T., Yamaguchi, C., Miyachi, T., Shoji, N., Matsuki, T., ... & Kamijima, M. (2020). Sexual difference in 2nd-to-4th digit ratio among 1.5-year-old Japanese children: A cross-sectional study of Aichi regional adjunct cohort of the Japan Environment and Children's Study (JECS-A). Early Human Development, 105050.)
 
 

Mothers, daughters and sons in Ghana

"This was a cross-sectional study from December 2020 to April 2021 involving 272 mothers, their daughters (n = 132) and their sons (n = 140). The right (2D:4DR) and the left (2D:4DL) digit ratios were measured using computer-assisted analysis. (...)
The mean ± SD 2D:4DR were 0.94 ± 0.04, 0.91 ± 0.04 and 0.90 ± 0.04 respectively for mothers, daughters and sons. The mean ± SD 2D:4DL was 0.93 ± 0.04, for mothers, 0.92 ± 0.05 for daughters and 0.92 ± 0.05 for sons. (...) The 2D:4DR of mothers was positively correlated with that of daughters (r = 0.332, P = 0.000) and that of sons (r = 0.233, P = 0.008). There are significant relationships between digit ratios in a mother–child population."
(Banyeh, M., Amidu, N., & Quaye, L. (2021). Second to fourth (2D: 4D) digit ratio and their relationships among a mother and child population in Ghana. Scientific Reports, 11(1), 1-11.)


Sexual dimorphism in the second-to-fourth digit ratio is not an artifact of differences in height

"Recently, a number of authors have claimed that sexual dimorphism in the second-to-fourth digit ratio (2D:4D) is simply dependent on digit length and is an artifact of allometry. The goal of our study is to verify the validity of these assumptions. The study sample comprised 7,582 individuals (3,802 men and 3,780 women) from three large world populations: Europeans (n = 3043), East Africans (n = 2844), and Central Asians (n = 1695).
(...)
[T]he 2D:4D magnitude and its sexual dimorphism remained stable throughout the ontogeny. To test for an allometric effect on 2D:4D, the average digit lengths were calculated. Both sex and population origin were permanent reliable predictors of 2D:4D, whereas average digit length was not. Height was applied as another measure of allometric effect on the limited sample (≤ 30 years) from the European population, along with sex and age. No allometric effect was observed in this case. We conclude that sex differences in 2D:4D are not an artifact of allometry."
(Butovskaya, M., Burkova, V., Apalkova, Y., Dronova, D., Rostovtseva, V., Karelin, D., ... & Batsevich, V. (2021). Sex, population origin, age and average digit length as predictors of digit ratio in three large world populations. Scientific reports, 11(1), 1-17.)


Self-reported 2D:4D ratios higher (and sometimes very incorrect) compared to measurements from photocopies

"In the present study, we compared 2D:4D from self-reported finger lengths measured directly from the fingers (S-R 2D:4D) and experimenter-measured finger lengths from photocopies of the fingers (photo 2D:4D). There were 329 participants (77 men, 252 women) recruited from a first-year undergraduate psychology pool. Compared to photo 2D:4D, (1) S-R 2D:4D tended to include some extreme values; (2) S-R 2D:4D was higher; (3) S-R 2D:4D showed weak similarities [with photo 2D:4D] which increased when extreme values of S-R 2D:4D were removed; (4) photo 2D:4D and S-R 2D:4D showed lower values for males compared to females but the dimorphism was significant for the former but not for the latter."
(source: A Comparison of Finger 2D:4D by Self-Report Direct Measurement and Experimenter Measurement from Photocopy: Methodological Issues, Noreen Caswell, John T. Manning; 4 February 2007, Arch Sex Behav, DOI 10.1007/s10508-007-9202-3, retrieved 27-7-2016)


Smartphone acceptable as instrument for measuring 2D:4D ratio, if used correctly

"This study explores the feasibility of using a Smartphone as an instrument for measuring finger length ratios. The approach taken in this study is to use the Smartphone camera to take freehand photos of the hand which is subsequently subjected to image analysis. [...] Experimental evaluations show that the most accurate measurements are achieved by resting the hand on a surface with the palm facing up. These results are comparable to those achieved with conventional procedures with an error of 1%."
(source: Measuring 2D:4D finger length ratios with Smartphone cameras, Frode Eika Sandnes ; Institute of information Technology, Faculty of Technology, Art and Design, Oslo and Akershus University College of Applied Sciences, Norway, 2014, DOI 10.1109/SMC.2014.6974161)

Computer software better than caliper better than ruler for measuring 2D:4D ratio (but all acceptable)

"Using different indirect methods (plastic ruler, caliper, computer software), three independent raters measured finger lengths of 60 participants. Generally, measurement precision [...] was acceptable for each method. However, precision estimates were highest for the computer software, indicating excellent measurement precision. Estimates for the caliper method were somewhat lower followed by ruler which had the lowest precision."
(source: Am J Hum Biol. 2009 Mar-Apr;21(2):188-91. doi: 10.1002/ajhb.20843., Comparing indirect methods of digit ratio (2D:4D) measurement, Kemper CJ1, Schwerdtfeger A.)

2D:4D increases slightly with age in children, rank order is stable

"We conclude that 2D:4D increases slightly with age in children with the effect less marked for the right hand (i.e. the hand which is likely to show the strongest association with prenatal steroids), 2D:4D is sexually dimorphic from an early age, and the rank order of 2D:4D is stable in children."

 (Trivers, Robert, John Manning, and Amy Jacobson. "A longitudinal study of digit ratio (2D: 4D) and other finger ratios in Jamaican children." Hormones and Behavior 49.2 (2006): 150-156.)


Inter-observer reliability in 2D:4D measures higher using photocopies than caliper

"Photocopying has been shown to be effective in previous human 2D:4D studies (Manning et al. 2001; Peters et al. 2002; Rahman & Wilson, 2003). The method produces measurements which correlate well with those obtained directly from the hands with callipers (Robinson & Manning, 2000) and tends to give lower 2D:4D ratios but with enhanced inter-observer reliability (Peters et al. 2002; Manning et al. 2005)."

Wrist position alters 2D:4D measures using photocopies

"The pilot study was designed to test the null hypothesis that wrist position (abducted, adducted or straight) does not alter 2D or 4D length measurements for an individual. Twelve independent participants (n = 6 males and n = 6 females) were selected randomly from a set of medical undergraduates in the library of the University of Nottingham Medical School. The purpose of the study was explained and each student consented to partake. Any student who had fractured, suffered trauma to, or had arthritis in, their 2D or 4D was excluded and students were asked to remove any rings from these digits.



The photocopier contrast was altered initially so that the proximal crease and distal finger tip were clearly visible. Three photocopies were taken from each student, the first with both hands in full abduction (radial deviation) at the wrist, the second with both hands in full adduction (ulnar deviation) and the third with a straight wrist, such that a line drawn along the length of the third digit extended between the radius and the ulna [the two long bones in the forearm]. In each position, the lengths of 2D and 4D were measured from the midpoint of the proximal crease, to the distal finger tip point, using digital callipers accurate to 0.01 mm. Differences between the 2D and 4D measurements were calculated for each of the three photocopies. For any individual, the minimum difference between photocopies was 0.05 mm and the maximum difference was 3.00 mm.

Despite the small sample sizes, significant differences between length measurements of the same digit were found for the three different hand positions. These indicated that abduction at the wrist favoured the 2D and adduction favoured the 4D. In a larger study (see Peters et al. 2002), similar significant differences were established."


2D:4D ratio in women not affected by menstrual cycle 

This study:
"In [righthanded women age 19-21] not taking oral contraceptives, there were significant differences over the menstrual cycle in both hands."
(Mayhew, T. M., et al. "Human 2D (index) and 4D (ring) digit lengths: their variation and relationships during the menstrual cycle." Journal of anatomy 211.5 (2007): 630-638.

was contradicted by this larger study:
"No differences in 2D:4D value across the menstrual cycle were detected either when right-hand, left-hand, and mean 2D:4D for both hands were analysed, nor when difference in the 2D:4D value between hands (Dleft-right) was evaluated. We documented that 2D:4D is independent of the phase of the menstrual cycle and these findings suggest that among naturally cycling women, a value of 2D:4D can be reliably obtained from measurements taken during any day of the menstrual cycle."
(Klimek, Magdalena, Urszula M. Marcinkowska, and Grazyna Jasienska. "Value of digit ratio 2D: 4D, a biomarker of prenatal hormone exposure, is stable across the menstrual cycle." Early Human Development 110 (2017): 21-24.)

Gender differences in 2D:4D ratios focussed on dominant hand

"[G]ender differences in [2D:4D] ratios appear to be focussed on the dominant hand."



Right-hand 2D:4D more reliable indicator of prenatal androgenisation than left-hand 2D:4D

"Right-hand 2D:4D might be a better indicator of prenatal androgenisation than left-hand 2D:4D. The view that 2D:4D has allometric properties (Kratochvil L, Flegr J. 2009. Differences in 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line. Biol Lett 5:643-646.) is not supported. Bone lengths contribute to the sex difference in 2D:4D. In addition, there might be a sex difference in fingers' soft tissue, which should be investigated."
(Hönekopp, Johannes, and Steven Watson. "Meta‐analysis of digit ratio 2D: 4D shows greater sex difference in the right hand." American Journal of Human Biology 22, no. 5 (2010): 619-630.)


2D:4D is not age-dependent

"2D:4D is not age‐dependent"
(Manning, John T., and Bernhard Fink. "Sexual dimorphism in the ontogeny of second (2D) and fourth (4D) digit lengths, and digit ratio (2D: 4D)." American Journal of Human Biology 30, no. 4 (2018): e23138.)


Palmar crease in men is differently placed than in women

"The results show that men have lower palmar-to-dorsal digit ratios than women, and this effect is significantly stronger for digit 2 than for digit 4. Thus, the present study supports the likelihood that differential placing of flexion creases in the digits contributes to the occurrence of sex differences in palmar 2D:4D."
(Kumar, Sanjay, Martin Voracek, and Maharaj Singh. "Differential placing of flexion creases contributes to sex differences in the second-to-fourth digit ratio (2D: 4D)." Frontiers in Endocrinology 10 (2019): 537.)


In Russia, the 2D:4D ratio of men increases from East to West

"The study was conducted on 263 young men (age range 17-30 years), including Russians, Armenians, Ob-Ugric and Buryats. The results revealed significant population differences in 2D:4D ratios on both hands, with lowest ratios for Asian sample, increasing in populations to the West. (...) Positive association between 2D:4D ratios on the right hand and Agreeableness in men with no respect to population origin was detected. This relationship becomes stronger, when controlling for aggressiveness."
(Victoria, Rostovtseva, Butovskaya Marina, and Mkrtchjan Ruzan. "2d: 4d, Big Fives and Aggression in Young Men of Caucasian, Ural and Asian Origin." Social Evolution & History 18, no. 1 (2019).)

Elbow carrying angle correlates with 2D:4D ratio in men and women

"Abstract: 
Background: The acute angle produced medially when the axis of the forearm deviates laterally from the long axis of the humerus, with the arm extended and the palm facing forward, is referred to as the carrying angle. Variations in the angle have clinical as well as pathological significance. 
(...)
Methods: 195 subjects with age varying from 12 to 32 years were studied. Carrying angle was measured using goniometer. Length of second and fourth digit was measured from distal palmar crease to tip of finger. 
Results: The result of the study showed that carrying angle is more in females than males on both sides. Lower values of carrying angle seen in males is strongly associated with longer ring finger and higher values of carrying angle seen in females associated with a longer index finger. There was only a moderately positive correlation between the carrying angle and fingertip lengths." 
(Biradar, Ravi Kumar, and H. M. Adarsha. "Study of elbow carrying angle and its relationship with the length of second and fourth digit." (2019).)


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