Hand preference and age in the United States

h'europ\~rhoiog,u, Vol.30, No. 7. pp 601 60X. 19Y2. Punted I" Great Bntan.

HAND

002X&3932,92$5.00+000 #c 1992 Pergamon PreaiLtd

PREFERENCE

AND AGE IN THE UNITED

STATES

AVERY N. GILBERT* and CHARLES J. WYSXKI~ *Givaudan-Roure

Corporation,

Teaneck, New Jersey, U.S.A.; and tMonell Philadelphia, Pennsylvania, U.S.A.

Chemical

Senses Center,

(Received 28 Junuury 1992; accepted 20 March 1992) Abstract-A survey of 1 177 507 U.S. men and women between the ages of 10 and 86 included questions regarding hand preference for writing and throwing. Three effects were observed. Individuals with at least some left motoric bias comprised a smaller percent of the population with advancing age. This finding provides large-scale confirmation of a previously described phenomenon. Among sinistrals, concordance for writing and throwing was 2.2 times as prevalent as left-writing with right-throwing, and 4.1 times as prevalent as right-writing with left-throwing. These sinistral subpopulations displayed distinct and stable prevalence prior to age 50 and changing patterns of prevalence subsequent to age 50. The results confirm a decrease with age in the prevalance of sinistrality, but indicate that age-specific rates of mixed- and left-handedness are distinct. The implications for hypotheses regarding age-related change in the prevalence of sinistrality are discussed.

INTRODUCTION A DECREASEwith age in the proportion ofleft-handers in the population has been reported by many investigators [2,4,6&S, 17,221. The various accounts offered for this phenomenon can be grouped under two headings: modification and elimination [S]. The most widely endorsed modification account posits a gradual and relatively recent lifting of societal sanctions against left-handed behaviors, especially with regard to writing and eating. In this account, age-related effects are seen as cohort effects [3, 183. The elimination account holds that left-handers suffer an elevated mortality rate. Various explanations have been advanced for this, including increased likelihood of fatal accidents, “ covert neuropathologies” [ 14, 151, and immune system dysfunction resulting from prenatal hormone exposure [9, lo]. The latter hypothesis has received much experimental attention, but few confirmations (see, e.g. Refs [19] and [24]). Some of the uncertainty about age-related change in hand preference is attributable to the size and segmentation of the study samples. A large sample is required to confidently estimate age trends among a low frequency target group, such as sinistrals. The largest studies to date were based on 5 199 subjects [6] and 6097 subjects [7]. Because very elderly subjects are more difficult to recruit than young ones, sample sizes among the aged are, in general, relatively small, further compounding the difficulty of surveying low frequency sinistrals. Previous studies grouped subjects into age brackets, most commonly by decade [2,&S], but also by broader categories [4, 17, 221. This technique increases the sample size for particular age ranges, but decreases the temporal resolution of the prevalence rate measures, making it *Address for correspondence: 07666. U.S.A.

A. N. Gilbert,

Givaudan-Roure

601

Corporation,

1775 Windsor

Road, Teaneck,

NJ

602

A. N. GILBEKT and C. J. WYSXKI

more difficult to accurately track handedness rates across time. This dilemma is magnified when age cohort sample size is reduced by including sex of respondent as an independent variable.The National Geographic Smell Survey provided an unprecedented opportunity to explore a number of potential determinants of odor perception, including pregnancy [ 121, geographic region [26] and aging [25]. Given its possible relation to lateral asymmetries in odor perception [l 1, reviewed in 131, the Smell Survey assessed hand preference with two questions. This report examines how hand preference varied with age in a large U.S. sample.

METHOD The Smell Survey (a questionnaire and microencapsulated set of odorants) was inserted in each copy of the September 1986 issue of the Nationul Groyraphic, and sent worldwide to 10.7 million members of the Society. The methods and technical features (e.g. odorant concentrations and complete questionnaire) were detailed in Ref. 1251; merely an outline is provided here. Participants provided their age. sex, country of residence, and ethnicity (response options: black, white, Asian. American Indian, Hispanic, other, prefer not to answer). They also reported which hand (left or right) they used to write, and to throw. Only respondents who answered both hand-use questions were retained for analysis. Based on their answers, respondents were assigned to four behavioral phenotypes: left-writing and left-throwing (LwL,). left-writing and right-throwing (LwR,), right-writing and left-throwing (R-L,), and right-writing and rightthrowing (RwR,). A worldwide total of I 420 000 usable surveys were returned (a 13% response rate). The results presented here are based on I I77 507 U.S. respondents between IO and 86 years of age. Ages outside this range were not included due to relatively small (< 500) sample sizes. Within the range, minimum sample size was 644 (age X6), and the maximum was 36 007 (age 39). The age and sex distribution of the sample population is illustrated in Fig. I. Women accounted for 56.4”/0 of the sample. Of the 96.2% of respondents who provided ethnic self-identification, 96.8% were white, I .O’% Hispanic. 0.9% Asian. 0.8% black, 0.2% American Indian, and 0.3% other. A rcadcrship survey showed that American members of the National Geographic Society are alIluent (mean 1987 household income $66 600) and well educated (73%) have attended college) [I]. Because the Smell Survey respondent was not necessarily the subscribing member of the household, these demographics only approximate those of the study sample. Because subjects were responding to a smell survey rather than a handedness survey, certain subject selection biascs that occur in handedness research [2l] may have been reduced

r 0

Females

n Males

/

20

30

40

50

60

70

80

Age, Years Fig. I. The frequency

distribution by age of male (filled bars. n = 513 304) and female (open bars. n = 664 203) respondents in the US. sample.

RESULTS Of the entire study population, 88.9% of respondents were concordantly right-handed (R,R,), and 11.1% showed evidence of left- or mixed-handedness (L,L,, L,R, or R,L,). A greater proportion of men (12.6%) than women (9.9%) evidenced a left motoric bias. An age

HANU

PKEFEKENCE

AEiD AGE IX THE UNITED

603

STATES

effect was evident in the prevalence of left- and mixed-handedness (Fig. 2). For both sexes, aggregate sinistrality was most prevalent at younger ages (14% for men, 12% for women), and least prevalent among the elderly (near 6% for both sexes). For women, the prevalence of aggregate sinistrality displayed a nearly linear negative slope across the age range (Fig. 2). For men, aggregate sinistrality was stable until the fifth decade, when a negative slope became apparent.

ob IO

20

I

I

m

40

Age, Fig. 2. Aggregate proportion

I 50

I 60

I 70

I 80

I

years

by age of mixed- and left-handed males (open circles) and females (filled circles).

The aggregate sinistral population consisted of three subpopulations. These differed in prevalence: 6.5% were LwL,, 3.0% were LwR, and 1.6% were RwL,. Thus, the subpopulation concordant for left-handedness outnumbered the two mixed-handedness subpopulations by factors of 2.2 and 4.1, respectively. When the sinistral subpopulations were examined separately, another set of age effects became evident. The relative proportion of each subpopulation changed across age cohorts. From age 10 to about age 50, the prevalence of L,L, (concordant left-handedness) was steady at 8--9% of the male population, and 667% of the female population (Fig. 3). Across ages 50-80, LwL, prevalence declined to about 2% for both sexes. Given the sex difference in prevalence among younger age cohorts, this result indicates a proportionally greater decline with age among males than females of the L,L, phenotype. LwR, mixed-handedness comprised 445% of the younger population, and only about 1% near age 70 (Fig. 3). RwL, mixed-handedness comprised ~2% of the younger population. Unique among the sinistral phenotypes, RwL, was more prevalent in cohorts from the sixth decade and beyond than in younger ones. By age 70, it was the most common sinistral phenotype (Fig. 3). Age-specific prevalence of the two mixed-handedness phenotypes was closely similar for men and women. This stands in distinct contrast to the sex difference in age-specific prevalence for the concordant left-handed phenotype (LwL,; see above). The time base of the graphs in Fig. 3 also represents a specific year of birth, e.g. age 40 corresponds to the birth cohort of 1946. Read this way (from right to left), the prevalence of the LwL, and RwL, subpopulations began to diverge at age 69 or 70, i.e. in the birth cohorts of 1916 and 1917. The L,L, proportion increased until the cohort of about 1937, and the RwL, proportion declined until the cohort of about 1929 (females) or 193 1 (males). The relative size of the sinistral subpopulations was compared across ethnic categories. The prevalence of LwL,, L,R, and RwL, phenotypes was identical for whites and blacks at 6.5, 3.0 and 1.6%, respectively. The corresponding proportions among American Indians

A. N.

604

GILBERT

and C. J. WYSOCKI

10

Fern&

0 LwLt * LwRt

8

v RwLt

Age,

years

Fig. 3. Proportion by age of males (top panel) and females (bottom panel) of L,R, mixed-handedness (filled circles), R,L, mixed-handedness (open triangles). and L,.L, concordant left-handedneaa (open circles).

were closely similar: 6.7,2.9 and 1.7’%. However, the proportions differed among Asians (4.1, 2.0, 3.3%) and Hispanics (5.3, 2.2, 1.6%). For both groups, left-handed writing was less prevalent than among whites, blacks or American Indians; for Asians, mixed-handedness with right-handed writing was more prevalent by a factor of 2.

DISCUSSION The National Geographic Smell Survey produced a sample large enough to permit year by year examination of trends in U.S. hand preference from ages IO through 86. The overall prevalence of sinistrality (mixed- and left-handedness) was similar to previous population estimates. In addition, there was a male-biased sex difference in this proportion that corroborated previous reports [7, 171. The observed cross-sectional decrease with age in the prevalence of aggregate sinistrality is also consistent with previous reports [2, 668, 17, 221. The results of this study revealed substantial variability with age in the three sinistral subpopulations. The subpopulations differed in prevalence among the youngest subjects, and in their change in prevalence across the age range. In older cohorts, the two phenotypes sharing a left hand writing preference (L,L, and L,R,) were less prevalent. In contrast, the sinistral phenotype with right hand writing preference (R,Lr) was more common in older cohorts. The subpopulation with the greatest cross-sectional decline was the L,L, men, who were initially the most prevalent group. Our documentation of substantial age-related differences in subpopulation prevalence underscores the importance of defining the extent of phenotypic variation in handedness.

HAND PREFERENCE

AND AGE IN THE UNITED

STATES

605

Phenotypic variation forms the empirical basis for theories of causation, but has received relatively little attention [21]. A recent experimental investigation of skill- and strengthbased measures of motor performance identified two sinistral subpopulations [20]. Inconsistent left-handers wrote and showed better fine motor performance with the left hand, but threw and were stronger with the right. Consistent left-handers (and right-handers) showed congruent skill and strength advantages for their preferred hand [20]. In our study, handedness was assessed by preferences for writing and throwing. To the degree these activities correspond to the skill and strength measures used by PETERS [20], they may reflect the same underlying phenotypic variation. The cross-sectional age trends documented here for the three left- and mixed-handedness subpopulations pose an interpretative challenge to certain theoretical models of sinistrality. In particular, the hypothesis of increased mortality among sinistrals [14, 151 does not provide an explanation for subpopulation variability. To take the present results into account, the mortality model should explain why mortality is higher among L,L, than R,L, and L,R, individuals, and why R,L, prevalence increases rather than decreases with age. To date, quantitative tests of the mortality model have combined mixed- and strongly left-handed subjects into one class for analysis, and have not addressed issues of subgroup variability [14, 151. Further, proponents of the model suggest that “left-banders are at greater risk of death at any given age” [ 151. This theoretical stance will have to be reconciled with the present finding that L,L, prevalence decreased only after age 50, while L,R, prevalence decreased steadily across the age range. Much the same burden of interpretation is placed on the prenatal hormone exposure variant of the mortality model [9, lo]. The challenge for proponents of that model is to differentially link the left- and mixed-handedness subpopulations described here to specific disease-related and age-specific mortality. In contrast, the present findings are consistent with a model that posits an historical reduction in socially mediated sanctions on left-handed writing beginning early in this century [3,1 X]. Given certain assumptions, this model can account for the variability among the three left- and mixed-handedness subpopulations. By assuming that natural throwing inclination is less susceptible to learned cultural influence, one can infer that R,L, and L,L, individuals are more intrinsically left-biased than L,R, individuals. R,LT individuals have presumably yielded to overt societal pressure and adopted right-handed writing, while maintaining left hand preference for activities under less direct societal sanctions. In contrast, L,L, individuals have maintained left-handed writing despite overt or covert societal pressure to conform. The easing of cultural sanctions against sinistral behaviors should result in smaller numbers of R,L, and greater numbers of L,L, individuals. Thus interpreted, Fig. 2 can be read, from right to left, as a record of the historical lifting of the repression of left-handed writing in the United States. That is, more recent birth cohorts show greater expression of intrinsic left motoric bias (higher prevalence of L,L, and L,R,), and reduced evidence of repressed left-handed writing (lower prevalence of R,L,). The more gradual increase in prevalence of L,R, (in comparison to L,L,) would reflect the weaker intrinsic left motoric bias of this group. Based on this hypothesis, the repression of left-handed writing in the United States would appear to have eased first around 1917, and been fully lifted by 1937. These dates correlate well with historical trends in the scientific attitude toward sinistrality as summarized by HARRIS [16]. Several reports published between 1911 and 1918 suggested that forcing left-handed children to write with their right hand interfered with the normal

A. N. GILBERTand C. J. WYXXKI

606

development of speech. This concern spread from psychologists and educators to the general public, as evidenced by articles in popular magazines from 1917 to 1922. Harris dates the change in pedagogical practice “to the period from approximately 19 15 to the early 1930’s” (p. 217). Ethnic variation in sinistral subpopulation prevalence also supports the cultural-sanctions model. Strictures on left-handed writing (perhaps driven by chopstick use) are stronger in China and Japan than in Western societies (see references in HARRIS [16]). Consistent with this observation, the prevalence of the left-handed writing phenotypes among Asian respondents was one-third less than among whites, blacks and American Indians. Further, the sinistral phenotype (RwL,) presumed to have yielded to societal pressure was twice as common in the Asian sample. Acknowledgements-We

thank

Mark S. Greenberg

for his comments

on an earlier draft of this paper.

REFERENCES United States Edition. 1. BETA RESEARCHCORPORATION.The Subscribing Households of National Geographic: National Geographic Society, Washington, DC, 1987. L. J. and KROONENBERG,P. M. Changes over time in the relationship between hand preference and 2. BEUKELAAR, writing hand among left-handers. Neuropsychologia 24, 301-303, 1986. 19,459462, 1981. 3. BRACKENRIDGE,C. J. Secular variation in handedness over ninety years. NeuropsychoIogia 4. BRITO, G. N. O., BRITO,L. S. 0. and PAUMGARTTEN,F. J. R. Effect of age on handedness in Brazilian adults is sex-dependent. Percept. Motor Skills 61, 829-830, 1985. a marker for decreased survival fitness. Psych. Bu[l. 109, 5. COREN, S. and HALPERN, D. F. Left-handedness: 90-106, 1991. 6. DELLATOLAS, G., TUBERT, P., CASTRESANA, A., et al. Age and cohort effects in adult handedness. Neuropsychologia 29, 255-261, 199 1. Neuropsychologia 24, I. ELLIS, S. J., ELLIS, P. J. and MARSHALL, E. Hand preference in a normal population. 157-163,

1988.

of adults. 8. FLEMINGER, J. J., DALTON, R. and STANDAGE, K. F. Age as a factor in the handedness Neuropsychologia 15,471413, 1911. associations with immune disease, migraine, and 9. GESCHWIND, N. and BEHAN, P. Left-handedness: developmental learning disorders. Proc. Nat1 Acad. Sci., USA 79, 5097-5100, 1982. Biological Mechanisms, Associations, and 10. GESCHWIND, N. and GALABURDA, A. M. Cerebral Lateralization: Pathology. MIT Press, Cambridge, MA, 1987. 11. GILBERT, A. N. and KARE, M. R. In Perfumes; Art, Science and Technology, P. M. MILLER and D. LAMPARSKY (Editors), pp. 127-149. Elsevier, London, 1991. assessment of olfactory experience during pregnancy. 12. GILBERT, A. N. and WYSOCKI, C. J. Quantitative Psychosom.

Med. 53, 693-700,

1991.

13. GILBERT, A. N., GREENBERG, M. S. and BEAUCHAMP,G. K. Sex, handedness, and side of nose modulate odor iudaments. Neuroasvcholoqia 27, 505-511, 1989. live longer? Nature 333, 213, 1988. 14. HALPERN, D. F. aii COR~N, S. Do right-handers and life span. New Enql. J. Med. 324,998, 1991. 15. HALPERN. D. F. and COREN. S. Handedness Behavioral Implicakons and Anomalies, S. COREN (Editor), pp. 195-258. 16. HARRIS, i. J. In Left-handedness: Elsevier, Amsterdam, 1990. of handedness in two samples of randomly 11. LANSKY. L. M.. FEINSTEIN, H. and PETERSON,J. M. Demography selected’adults (N=2083). Neuropsychologia 26, 465477,1988. 18 LEVY, J. In Hemispheric Function in the Human Brain, S. J. DIMONDand J. G. BEAUMONT(Editors), pp. 121- 183. Elek Science, London, 1974. homosexuality, HIV 19. MARCHANT-HAYCOX, S. E., MCMANUS, I. C. and WILSON, G. D. Left-handedness, infection and AIDS. Cortex 27, 49-56, 1991. of non-pathological left-handers poses problems for theories of handedness. 20. PETERS, M. Subclassification Neuropsychologia 28, 279-289, 1990a. Behaoioral Implications and Anomalies, S. COREN (Editor), pp. 167-192. 21. PETERS, M. In Left-handedness: Elsevier, Amsterdam, 1990b. 22. PLATO. C. C.. Fox. K. M. and GARRUTO, R. M. Measures of lateral functional dominance: hand dominance. Hum. Viol. 56, 259-275, 1984. 23. PORAC, C., COREN, S. and DUNCAN, P. Life-span age trends in laterality. J. Gerontol. 35, 715-721, 1980.

607

HAND PREFERENCE AND AGE IN THE UNITEDSTATES

24. STANTON, W. R., FEEHAN, M., SILVA, P. A. and SEARS, M. R. Handedness and allergic disorders in a New Zealand cohort. Cortex 27, 131-135, 1991. 25. WYSOCKI, C. J. and GILBERT, A. N. In Chemical Senses and Nutrition in Aging, C. MURPHY, W. S. CAIN and D. M. HEGSTED (Editors), pp. 12-28. Ann. N.Y. Acad. Sci. 561, 1989. 26. WYSOCKI, C. J., PIERCE,J. D. JR. and GILBERT, A. N. In Smell and Taste in Health and Disease, T. V. GETCHELL, R. L. DOTY, L. M. BARTOSHUKand J. B. SNOW, JR. (Editors), pp. 287-314. Raven Press, New York, 1991.

ADDENDUM

I

Age-speciJic frequencies of handedness phenotypes for female subjects Age

LwLT

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

95 140 197 286 325 406 439 336 311 265 270 328 364 386 471 603 645 859 929 1004 1215 1170 1291 1291 1299 1375 1289 1256 1251 1338 1073 921 825 959 793 665 600 562 585

LwRT 54 71 148 184 205 273 303 257 208 175 163 198 254 271 321 422 431 542 561 630 616 692 680 688 660 716 609 630 582 627 502 427 418 438 356 309 296 255 240

RwLT

RwRl

Age

26 31 50 62 54 57 86 59 48 44 42 53 51 64 69 94 96 124 106 131 176 152 173 180 166 168 150 177 171 174 153 157 154 162 139 129 125 129 122

1248 1983 3022 4190 4461 5347 6012 4912 4066 3571 3481 4190 4545 5486 6690 8409 9520 10 886 12 784 13 760 15 675 15 433 17 215 17 127 17 121 17 475 16 042 16 103 16 451 17 580 14 484 11311 11963 12 445 9934 9813

49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 16 II 78 79 80 81 82 83 84

8749 8264 8526

85 86

Lb 501 512 519 497 509 513 541 517 459 446 445 480 381 411 324 313 350 272 206 213 171 151 128 135 98 85 72 54 60 50 42 42 22 18 22 9 9 8

LwRT 217 243 209 196 186 163 221 172 165 164 177 159 111 138 90 90 104 69 60 51 37 45 40 39 22 19 20 17 13 18 10 12 6 5 1 4 3 2

RwLT 119 144 125 132 125 135 160 158 189 191 199 258 185 245 217 229 281 200 175 202 172 159 103 140 113 80 91 85 53 56 36 42 19 18 17 17 16 6

Rwb 8069 9244 7961 8596 8451 8570 9779 9466 9118 9407 9303 10 783 8559 9851 8763 8588 9768 7515 6490 6416 5606 5990 4382 4310 3644 3263 3089 2441 2069 1884 1489 1449 903 786 642 482 312 313

A. N. GILBERT and C. J. WYSOCKI

608

ADDENDUM Age-specific frequencies

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

95 151 226 298 361 410 471 388 305 261 285 316 303 399 421 521 585 690 842 925 1091 1075 1233 1249 1330 1380 1345 1309 1311 1471 1142 943 999 1027 857 804 676 659 617

42 91 137 157 183 225 274 210 191 144 138 173 164 208 216 263 273 352 419 446 564 525 582 552 629 607 603 561 596 629 508 406 390 419 347 324 308 265 243

of handedness

21 29 36 52 62 78 79 70 46 40 41 43 58 49 85 83 99 117 147 117 166 175 185 180 161 177 189 183 192 233 210 162 177 180 168 164 139 128 148

II

phenotypes for male subjects

1077 1503 2290 3179 3428 4340 4900 3945 3154 2515 2541 2929 3237 3808 4303 5373 6109 6931 8411 8970 10 651 10 713 11 587 12 281 12 292 12 823 12 141 11947 12 808 13 955 11414 9430 9815 10 480 8566 7983 7128 6714 6636

49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 13 74 75 76 77 78 79 80 81 82 83 84 85 86

527 564 489 412 495 469 537 493 526 487 430 459 358 413 339 264 338 276 221 220 202 180 154 140 104 93 100 84 45 32 30 36 25 16 14 10 18 4

214 229 157 180 186 197 189 199 189 137 142 130 131 138 107 114 98 95 67 65 62 54 35 31 31 21 25 36 14 16 7 10 10 8 12 1 3 3

115 107 102 133 111 127 165 179 163 188 205 231 179 207 226 198 252 219 195 198 181 180 164 153 136 107 113 98 49 77 65 52 37 37 18 22 11 9

5992 6656 5732 6054 6016 6083 6784 6934 6477 6811 6759 7252 6274 7392 6591 6502 7257 6130 5132 5425 4728 4748 3824 3917 3280 2855 2600 2225 1861 1674 1398 I278 914 764 632 462 393 299