The epidemiology of left-handedness in a hospital population

Progression of symptomatic bilateral rotator cuff disease

Background

Prior studies have demonstrated that conservatively treated rotator cuff tears and rotator cuff tendinopathy may continue to progress. It is unclear whether that rate of progression differs between sides in patients with bilateral disease. This study evaluated the likelihood of progression of rotator cuff disease as confirmed via magnetic resonance imaging (MRI) in individuals with symptomatic bilateral pathology, treated conservatively for a minimum of 1 year.

Methods

We identified patients with bilateral rotator cuff disease confirmed via MRI within the Veteran's Health Administration electronic database. A retrospective chart review via the Veteran's Affairs electronic medical record was performed. Progression was determined using 2 separate MRIs with a minimum of 1 year apart. We defined progression as (1) a progression from tendinopathy to tearing, (2) an increase from partial-thickness to full-thickness tearing, or (3) an increase in tear retraction or tear width of at least 5 mm.

Results

Four hundred eighty MRI studies from 120 Veteran's Affair patients with bilateral, conservatively treated rotator cuff disease were evaluated. Overall, 42% (100/240) of rotator cuff disease had progressed. No significant difference was found between progression of right vs. left rotator cuff pathology, with right shoulder pathology progressing at a rate of 39% (47/120), while left shoulder disease progressed at a rate of 44% (53/120). The likelihood of disease progression was associated with less initial tendon retraction (P value = .016) and older age (P value = .025).

Conclusions

Rotator cuff tears are no more likely to progress on the right, as compared to the left side. Older age and less initial tendon retraction were found to be predictors of disease progression. These suggest that higher activity level may not associate with greater progression of rotator cuff disease. Future prospective studies evaluating progression rates between dominant vs. nondominant shoulders are warranted.

Epidemiology and Fracture Patterns of Traumatic Phalangeal Fractures

Background:

Despite the relatively high incidence of phalangeal fractures, there is an imperfect understanding of the epidemiology and anatomical distribution of these fractures. This study describes the patient characteristics, anatomic distribution, and detailed fracture patterns of phalangeal fractures among a large adult cohort in the United States.

Methods:

A retrospective study was performed among patients with phalangeal fractures in the United States between January 2010 and January 2015. Included patients were 18 years old or older and had a diagnosis of a phalangeal fracture. A total of 2140 phalangeal fractures in 1747 patients were included, and a manual chart review was performed to collect epidemiological and radiographic information. Fractures were classified based on location and fracture pattern.

Results:

The median age at the time of injury was 45 years (interquartile range, 30–57), and 65% of patients were men. The small finger had the highest incidence of fractures (26%) followed by the ring finger (24%). Distal and proximal phalanges demonstrated the highest incidence of fractures at 39% each. The dominant hand was affected in 44% of cases. Eighteen percent of fractures were due to a work-related trauma mechanism, and the most common mechanism of injury was blunt trauma (46%).

Conclusion:

This study provides a detailed overview of the anatomic distribution and fracture patterns of phalangeal fractures in an adult US population and, thus, may aid hand surgeons treating these injuries.

Lateralization of Squamous Cell Carcinomas in the Head-Neck Region

Earlier studies have shown the lateralization of several immune disorders, including herpes zoster infection and breast cancer. We investigated whether there is lateralization of squamous cell carcinomas in the head-neck region and a relation of handedness with this cancer. Analysis showed right-sided lateralization of head-heck cancers in right-handed patients and vice versa in left-handed ones and a higher rate of left-handedness in patients with squamous cell cancer. Associations among left-handedness, squamous cell carcinoma, and its lateralization may result from a genetic togetherness.

Left handedness: Facts and Figures across Cultures

Approximately 10% of human beings are left handed, although the incidence rate dif fers as a function of sex, age, and culturelgeographical locations. Studies reveal that (a) the incidence of left handedness is more common in Euro-American than in Orien tal ( India, Japan, China) cultures, (b) the prevalence of left handedness throughout the historical era is best explained by genetic models, (c) left handedness is associated more with immune and psychopathological disorders, and (d) sanctions against left hand use are rooted to the belief system and social construction in a given culture. These obser vations were made in this article to ascertain the issues related to left handedness, espe cially in socio-cultural contexts.

Genetic factors and breast cancer laterality

BACKGROUND

Women are more likely to develop cancer in the left breast than the right. Such laterality may influence subsequent management, especially in elderly patients with heart disease who may require radiation therapy. The purpose of this study was to explore possible factors for such cancer laterality.

METHODS

In this work, clinical data for consecutive patients with histologically confirmed breast cancer were reviewed, with emphasis on clinical presentation and family history.

RESULTS

Between 2005 and 2012, 687 patients with breast cancer were seen. Two women with incomplete data and eleven men were excluded. In total, 343 (50.9%) patients presented with left breast cancer, 311 (46.1%) with right breast cancer, and 20 (3.0%) with simultaneous bilateral malignancy. There were no significant differences between the three groups, especially in regards to clinical presentation and tumor characteristics. A total of 622 (92.3%) patients had unilateral primary, 20 (3.0%) had simultaneous bilateral, and 32 (4.7%) had metachronous primary breast cancer with subsequent contralateral breast cancer after 7.5-236 months. The worst 10-year survival was for bilateral simultaneous (18%) compared with unilateral (28%) and metachronous primaries (90%). There were no differences in survival in relation to breast cancer laterality, handedness, and presence or absence of a family history of cancer. There were significant similarities between patients and first-degree relatives in regards to breast cancer laterality, namely same breast (30/66, 45.5%), opposite breast (9/66, 13.6%), and bilateral cancer (27/66, 40.9, P=0.01163). This was more evident among patients and their sisters (17/32, 53.1%) or mothers (11/27, 40.7%, P=0.0689). There were also close similarities in relation to age at initial diagnosis of cancer for patients and their first-degree relatives for age differences of ≤5 years (48/166, 28.9%), 6-10 years (34/166, 20.5%), and >11 years (84/166, 50.6%, P=0.12065).

CONCLUSION

High similarities between patients and their first-degree relatives in regards to cancer laterality and possibly age at initial diagnosis of cancer may suggest an underlying inherited genetic predisposition.

The study of radiosensitivity in left handed compared to right handed healthy women

Background

Radiosensitivity is an inheriting trait that mainly depends on genetic factors. it is well known in similar dose of ionizing radiation and identical biological characteristics 9–10 percent of normal population have higher radiation response. Some reports indicate that distribution of breast cancer, immune diseases including autoimmune diseases as example lupus, Myasthenia Gravies and even the rate of allergy are more frequent in left handed individuals compared to right handed individuals. The main goal of the present study is determination of radiosensitivity in left handed compared to right handed in healthy women by cytokinesis blocked micronuclei [CBMN] assay.

5 ml peripheral fresh blood sample was taken from 100 healthy women including 60 right handed and 40 left handed. The age of participants was between 20–25 old years and they had been matched by sex. After blood sampling, blood samples were divided to 2 groups including irradiated and non-irradiated lymphocytes that irradiated lymphocytes were exposed to 2 Gy CO-60 Gama rays source then chromosomal aberrations was analyzed by CBMN [Cytokinesis Blocked Micronuclei Assay].

Results

Our results have shown radiosensitivity index [RI] in left-handers compared to right-handers is higher. Furthermore, the mean MN frequency is elevated in irradiated lymphocytes of left-handers in comparison with right-handers.

Conclusion

Our results from CBMN assay have shown radiosensitivity in the left handed is higher than right handed women but more attempts need to prove this hypothesis.

Left-handedness is statistically linked to lifetime experimentation with illicit drugs

Handedness has been linked to an enhanced risk of alcohol abuse, while less is known about other drugs. A convenience sample of 1004 male and female Italian participants (females=58%) from the general community (18 to 65 years old: average age = 30; standard deviation = 10, median = 25) was asked about: handedness (preference in writing); lifetime use of alcohol, tobacco, and illicit drugs; levels of psychological distress, as measured by the General Health Questionnaire (GHQ); and levels of delusion proneness, as measured by the Peters et al. Delusions Inventory (PDI). Overall, 92 individuals (9.2%) were classified as left-handed, with no significant difference reported among genders. Lifetime use of illicit drugs, primarily cannabis, was reported by 20% of the sample. In a multiple logistic regression analysis, after taking into account sex, age, and caseness on GHQ and PDI, left-handed people in the sample were statistically more likely to report lifetime experimentation with heroin, ecstasy/amphetamine, and, marginally, hallucinogens, but not alcohol or tobacco. Different mechanisms might contribute to an explanation of greater lifetime experimentation with some illicit drugs among left-handed people as compared to right-handed people. However, replications with clinical samples are necessary before any definitive statements can be made.

Brain asymmetry, immunity, handedness

The principle of symmetry-asymmetry is widely presented in the structural and functional organization of the nonliving and living nature. One of the most complex manifestations of this principle is the left-right asymmetry of the human brain. The present review summarizes previous and contemporary literary data regarding the role of brain asymmetry in neuroimmunomodulation. Some handedness-related peculiarities are outlined additionally. Brain asymmetry is considered to be imprinted in the formation and regulation of the individual’s responses and relationships at an immunological level with the external and internal environment. The assumptions that the hemispheres modulate immune response in an asymmetric manner have been confirmed in experiments on animals. Some authors assume that the right hemisphere plays an indirect role in neuroimmunomodulation, controlling and suppressing the left hemispheric inductive signals.

[Social aspects of left-handedness]

Throughout human history left-handedness has been considered as sinful. It has been associated with the devil, weakness, female gender, unhealthiness, evil, something that has to be turned to a "good"--right side by force. Left-handedness is being more and more acceptable at rational level, but in everyday life it is still considered to be unusual if someone writes with the left hand. Lessening of the number of lefthanders is associated with ageing. There are about 13% lefthanders among people in twenties and less than 1% lefthanders among those in eighties. This finding may be explaned with more pronounced socio-cultural pressure on left-handed people in the past, compared to nowadays. On the other hand, this may also support the hypothesis about a reduced life span of lefthanded people. With cross-exercising of left-handedness, certain typical characteristics and behavioural patterns appear in these people. This was a sort of provoked behaviour and an attack on the integrity of an emotional attitude toward oneself. Stuttering may also appear as a consequence of unsuccessful cross-exercising of left-handedness. The hypothesis about left-handedness as an advantage is supported with the reports about relatively more lefthanders in some specific groups such as: mathematicians, sculptors, architects, painters, musicians, actors, tennis players, as well as famous army commanders and rulers.

[Left-handedness and health]

Hand dominance is defined as a proneness to use one hand rather than another in performing the majority of activities and this is the most obvious example of cerebral lateralization and an exclusive human characteristic. Left-handed people comprise 6-14% of the total population, while in Serbia, this percentage is 5-10%, moving from undeveloped to developed environments, where a socio-cultural pressure is less present. There is no agreement between investigators who in fact may be considered a left-handed person, about the percentage of left-handers in the population and about the etiology of left-handedness. In the scientific literature left-handedness has been related to health disorders (spine deformities, immunological disorders, migraine, neurosis, depressive psychosis, schizophrenia, insomnia, homosexuality, diabetes mellitus, arterial hypertension, sleep apnea, enuresis nocturna and Down Syndrome), developmental disorders (autism, dislexia and sttutering) and traumatism. The most reliable scientific evidences have been published about the relationship between left-handedness and spinal deformities in school children in puberty and with traumatism in general population. The controversy of other results in up-to-now investigations of health aspects of left-handedness may partly be explained by a scientific disagreement whether writing with the left hand is a sufficient criterium for left-handedness, or is it necessary to investigate other parameters for laterality assessment. Explanation of health aspects of left-handedness is dominantly based on Geschwind-Galaburda model about "anomalous" cerebral domination, as a consequence of hormonal disbalance.

Differences by Sex and Handedness in Right and Left Femur Bone Mineral Densities

Left-handedness was reported to be a risk factor for accident-related injuries, head injuries, traumatic brain injuries, sport-related injuries, and bone breaks and fractures. As decreased bone mineral density is a good marker of bone fractures, the femoral bone mineral densities of normal left-handed university students were compared with those of right-handed students. Hand preference of 66 men and 47 women was assessed using the Edinburgh Handedness Inventory. Measures of bone mineral density with a Hologic QDR-4500W (S/N 48403) densitometer showed bone mineral densities of both right and left proximal femur regions were higher in right-handed than in left-handed students. These results are consistent with the claim that left-handed participants had higher trauma and injury risk. Also, these results may explain the sex-related differences by handedness for susceptibility in accident-related injuries such as bone fractures.

Handedness Correlates with Actigraphically Measured Sleep in a Controlled Environment

The relationship between hand preference and duration of sleep was assessed in 40 healthy subjects using self-report estimates, sleep diaries, and wrist activity monitors during an uncontrolled 7-day at-home phase and during a controlled overnight stay in a sleep laboratory. Handedness was unrelated to any index of sleep duration when assessed in the unregulated home environment. In the controlled environment of the laboratory, however, greater right-hand dominance was positively correlated with more minutes of obtained sleep and greater sleep efficiency. Findings were consistent with previous reports which suggest measures of brain lateralization may be related to sleep and health but further suggest that these relationships may be easily obscured by extraneous environmental factors when assessed in an uncontrolled setting.

Handedness in Great Britain

Two large British databases of handedness assessed by writing hand at 10-11 years of age were analysed by geographical region. Left-handedness was found to vary significantly across regions according to one survey but not the other. In both data sets, left-handed writing was significantly more frequent in England than in Scotland and Wales combined. Possible reasons for this difference are discussed.

Sex and eyedness in a sample of Turkish high school students

The relationship of sex with eyedness was examined in 176 boys and 129 girls ages 15 to 21 years (M = 16.9 yr., SD = 1.8) in Turkish high schools. Sex was significantly associated with handedness; the rate of left-handedness was 10.8% in boys and 2.3% in girls and was not related to eyedness. Rate of left-eyedness in the sample was 7.9% for boys and 8.5% for girls. One may wonder whether eyedness shows a reverse sex effect, less than handedness, but methods of measurement must be compared.

Hand preference for writing and associations with selected demographic and behavioral variables in 255,100 subjects: the BBC internet study

In an Internet study unrelated to handedness, 134,317 female and 120,783 male participants answered a graded question as to which hand they preferred for writing. This allowed determination of hand preference patterns across 7 ethnic groups. Sex differences in left-handedness were found in 4 ethnic groups, favoring males, while no significant sex differences were found in three of the groups. Prevalence of left-handedness in the largest of the ethnic groups (self-labelled as "White") was comparable to contemporary hand preference data for this group [Gilbert, A. N., & Wysocki, C. J. (1992). Hand preference and age in the United states. Neuropsychologia, 30, 601-608] but the prevalence of left-handedness in individuals >70 years of age was considerably higher in the present study. Individuals who indicated "either" hand for writing preference had significantly lower spatial performance (mental rotation task) and significantly higher prevalence of hyperactivity, dyslexia, asthma than individuals who had clear left or right hand preferences, in support of Crow et al. [Crow, T., Crow, L., Done, D., & Leask, S. (1998). Relative hand skill predicts academic ability: global deficits at the point of hemispheric indecision. Neuropsychologia, 36, 1275-1282]. Similarly, an association of writing hand preference and non-heterosexual orientation was clearest for individuals with "either" writing hand responses. We conclude that contradictions in the literature as to whether or not these variables are linked to handedness stem largely from different definitions of hand preference. Due to a lack of statistical power in most studies in the literature, the "either" hand writing preference group that yielded the most salient results in this study is not normally available for analysis.

Handedness, eyedness, and crossed hand-eye dominance in male and female patients with migraine with and without aura: a pilot study

The possible relationships of migraine to left-handedness and left-eyedness, as well as sex and aura-related differences, were examined. 146 migraine patients (M age=32.1 yr., SD=9.5) and 141 controls (M age=30.0 yr., SD=9.3) participated. Hand preference was assessed by the modified version of the Edinburgh Handedness Inventory. Ocular dominance was measured by means of the near-far alignment test. Migraine diagnoses were made on the basis of criteria provided from the International Headache Society. In the overall sample and in women, left-handedness and left-eyedness were not significantly correlated with migraine. In men, the incidence of left-handedness and left-eyedness were significantly higher in patients than in controls. The presence of aura in patients with migraine was significantly associated with the incidence of left-eyedness and crossed hand-eye dominance, but not handedness, for the total sample and women. These results suggest that there may be a tendency towards anomalous dominance, especially left-eyedness, in migraine patients particularly those with aura.

Family size, miscarriage-proneness, and handedness: tests of hypotheses of the developmental instability theory of handedness

The handedness theory of Yeo and Gangestad (1993) posits that moderate right-handedness is the modal manifestation of genetic handedness and that ''developmental instability'' produces deviations from modal handedness. It is also suggested (1) that sinistral parents may produce fewer offspring than do dextral parents; and (2) that sinistral mothers may be more prone to miscarriages than are dextral mothers. In line with these hypotheses, Gangestad et al. (1996) reported that a human leukocyte antigen (B8) was related to both left-handedness and to reduced offspring number in their study. They also found that left-handedness was related to the human leukocyte antigen DR3, and Yeo and Gangestad (1998) noted that this antigen has been found by Christiansen et al. (1996) to be associated with an increased risk of spontaneous abortion in women. We assessed the first hypothesis through a study of the family sizes of 2083 families with two right-handed parents and 502 families having one or more left-handed parents; we assessed the second hypothesis from miscarriage history data supplied by 300 dextral and 52 sinistral mothers. Results supported the developmental instability theory with respect to the hypothesis regarding family size, but not with respect to the hypothesis regarding miscarriage-proneness.

Preferential distal radius fracture in right-handed individuals presenting to an ED

The purpose of this study was to determine whether there is a lateralizing predisposition toward injury in right hand-dominant (RHD) individuals. The distal radius fracture was used as the injury for evaluation because it is easily defined and can be objectively documented by roentgenography. A prospective case-series design was used to include consecutive RHD patients with a distal radius fracture. There were 86 women with an average age of 63.1 +/- 17.9 years and 41 men with an average age of 44.0 +/- 17.6 years with a significant difference between ages (P <.01). Overall, there were 50 right and 77 left distal radius fractures, which was significantly different than a 50:50 split (P <.025). Stratification and logistic regression analysis revealed that age (dichotomized into age greater than 57 or other) and not gender was a significant factor in the determination of left versus right distal radius fracture. No interaction between age and gender was found. After adjustment for gender, the odds of developing a left compared with right distal radius fracture was 2.3-fold greater for the older compared with the younger age group (95% confidence interval, 1.0-5.2). Preliminary evidence suggests a lateralizing predisposition for left distal radius fractures in older compared with younger individuals who are RHD. If this data holds up, finding the etiology/mechanism of this predisposition might help in designing environments to minimize the impact of this injury pattern in the slightly older individual.

Left-handedness as a risk factor for fractures

Left-handedness has been associated with increased fracture risk in a small number of previous studies. This study reports risks for fractures at the proximal humerus, distal forearm, pelvis, foot, and shaft of the tibia/fibula according to handedness in a case-control study conducted from October 1996 to May 2001 among members of Northern California Kaiser Permanente. Handedness was assessed by questionnaire for 2,841 cases and 2,192 controls, and subjects were categorized as left-handed, right-handed, ambidextrous, or forced to switch from the left to the right hand. Compared to right-handedness, left-handedness was most strongly associated with an increased risk for proximal humerus fractures (adjusted odds ratio (OR)=2.00, 95% confidence interval (CI) 1.33 to 3.01) and less definitively with fractures of the distal forearm (adjusted OR=1.28, 95% CI 0.92 to 1.80), foot (adjusted OR=1.17, 95% CI 0.82 to 1.65), and pelvis (adjusted OR=1.40, 95% CI 0.71 to 2.74). Ambidextrous individuals had elevated risks for fractures of the distal forearm (adjusted OR=2.99, 95% CI 1.42 to 6.30), foot (adjusted OR=2.59, 95% CI 1.13 to 5.97), shaft of the tibia/fibula (adjusted OR=3.91, 95% CI 1.01 to 15.17), and proximal humerus (adjusted OR=2.37, 95% CI 0.85 to 6.65) when compared with right-handed individuals. Those individuals forced to use the right hand demonstrated no increased risk for fractures at any site. These results suggest that handedness does influence fracture risk, but the reasons for this increased risk are unclear.

Single-voxel proton MR spectroscopy of right versus left hippocampi in PTSD

Previous magnetic resonance (MR) volume imaging and proton MR spectroscopy studies have suggested a reduction in the hippocampal size and/or neuronal/axonal density in posttraumatic stress disorder (PTSD). The lack of agreement on the laterality of the hippocampal dysfunction prompted this study. A total of 20 veterans (18 men and two women) and one female non-veteran participated in this study conducted in accordance with approved human study protocols. Six of the male veterans and the female non-veteran were without PTSD. Vietnam veterans formed a large subset of the study subjects. Single-voxel proton MR spectra were obtained from the hippocampal region bilaterally on a clinical MR scanner operating at 1.5 T. Analysis of the proton MR spectra showed a decrease in hippocampal NAA/creatine ratio in PTSD subjects significantly higher on the left than the right for the entire study group, as well as for the Vietnam subset. It was concluded that the hippocampal dysfunction in PTSD is lateralized with the left side being more impaired than the right.

Cognitive abilities in left-handers: writing posture revisited

Among 1848 young men appearing before the Danish draft board, 232 (13%) were left-handed. Of these, 118 (51%) used an inverted, or hook-like, writing posture, 49 (21%) used a non-inverted posture and the remaining 65 (28%) could not be categorized. There were no differences between left- and right-handers on a battery of four cognitive tests. However, inverted left-handers performed significantly or near-significantly better than the non-inverted left-handers on two of the four tests and significantly better on the total score for the test battery. These results support the contention that the inverted posture is adaptive for left-handers and suggest that it may be more likely to be adopted by those with better cognitive abilities. Our findings conflict with earlier reports from two decades ago, however, and the association may therefore be socially and culturally dependent.

Handedness in Colombia: Some associated conditions

As part of a national neuroepidemiological study a population-based sample of 6941 subjects, 10 years of age or older, was selected in five different regions in Colombia (South America). Overall, 91.65% of the participants (90.6%) of the males; 92.7% of the females) considered themselves as right-handers. Handedness was significantly correlated with education in men but not in women. Handedness was not associated with age. Prevalence of history of loss of consciousness, tremors, difficulties with speech, and traumatic head injury was observed to be higher in non-handers than in right-handers. This finding was particularly evident in men. Implications of current results are analysed.

Sexual orientation and handedness in men and women: a meta-analysis

Recent findings suggest that sexual orientation has an early neurodevelopmental basis. Handedness, a behavioral marker of early neurodevelopment, has been associated with sexual orientation in some studies but not in others. The authors conducted a meta-analysis of 20 studies that compared the rates of non-right-handedness in 6,987 homosexual (6,182 men and 805 women) and 16,423 heterosexual (14,808 men and 1,615 women) participants. Homosexual participants had 39% greater odds of being non-right-handed. The corresponding values for homosexual men (20 contrasts) and women (9 contrasts) were 34% and 91%, respectively. The results support the notion that sexual orientation in some men and women has an early neurodevelopmental basis, but the factors responsible for the handedness-sexual orientation association require elucidation. The authors discuss 3 possibilities: cerebral laterality and prenatal exposure to sex hormones, maternal immunological reactions to the fetus, and developmental instability.

Left-handedness in relation to breast cancer risk in postmenopausal women

Breast cancer risk may be influenced by intrauterine exposure to steroid hormones. We evaluated left-handedness, a marker of intrauterine hormone exposure, in relation to breast cancer risk in our population-based, case-control study. Case women 50-79 years of age with a first diagnosis of invasive breast cancer were ascertained through statewide cancer registries in Wisconsin, Massachusetts, and New Hampshire. Control women were identified in each state through lists of licensed drivers (for ages 50-64) and Medicare beneficiaries (for ages 65-79), and selected at random to correspond with the age distribution of case women. Exposure information, including handedness, was obtained through a telephone interview. Our results indicated a modest association between left-handedness and breast cancer risk (OR = 1.42; 95% CI = 1.10-1.83). The effect of left-handedness was modified by age; we observed the greatest risk ratio in the oldest age group. Left-handedness was not associated with breast tumor laterality. Our results are consistent with the hypothesis that intrauterine hormone exposures play a role in the development of breast cancer.

The association between switching hand preference and the declining prevalence of left-handedness with age

OBJECTIVES

This study determined the prevalence of left-handedness and of switching hand preference among innately left-handed subjects.

METHODS

Subjects of Swiss nationality (n = 1692), participating in a population-based survey in Geneva, Switzerland, completed a questionnaire on innate hand preference and current hand preference for writing.

RESULTS

From 35 to 44 years of age to 65 to 74 years of age, the prevalence of innate left-handedness declined from 11.9% to 6.2% (trend P = .007). In these same age groups, the proportion of innately left-handed subjects who switched to the right hand for writing increased from 26.6% to 88.9% (trend P = .0001).

CONCLUSIONS

Across generations, we found an increase in the prevalence of switching hand preference among innately left-handed subjects. This phenomenon could be explained by social and parental pressure to use the right hand.

Handedness and sex differences in intelligence: evidence from the medical college admission test

Our analysis of Medical College Admission Test subtest scores by writing hand preference and sex suggests that (a) right hemispheric dominance is associated with intellectual giftedness in verbal reasoning (left-handers obtained higher scores on the verbal reasoning test and were overrepresented in the upper tail of the distribution), (b) different patterns of brain lateralization are associated with different subcomponents of cognition (right-handers scored higher, on average, on the writing test and were overrepresented in the upper tail of the distribution), and (c) men generally score higher than women on tests of scientific knowledge (the most striking differences between men and women were on the biological and physical science tests).

Some aspects of self-reported hand preference

The aim of the present study was to compare self-reported handedness with the directly tested hand preference using a 10-item battery in sample of 1223 students. The question assessing self-reported handedness was whether you are a left- or a right-hander or you use both hands equally. Responses indicate that self-reported handedness is a crude but possible method of measurement. Female right-handers showed the best agreement.