RESEARCH REPORT d12
National
organization of
Mothers
suBJECT:
HANDEDNESSIN MULTIPLES SURVEY
Of
RESEARCHER:
Nationa.lOrganizationof Mothersof Twins Clubs,lnc.
Twins
Clubs, Inc'
DATE:
1e87
PURPOSE:
in multiplesby twin type as well
The purposeof this surveywasto examinehandedness
in singletonsiblingsandparents'
as handedness
METHOD:
of their multiples,siblingsand themselves'
Parentswere surveyedaboutthe handedness
BACKGROUNDINFORMATION:
I.
This surveywirsdividedinto five questions:
A.
ageof multipleswas5'4 years
Age--average
B.
Zygosity
l. 36% wete identicaltwins
2. 58% wercfraternaltwins and triplets
3. 6% wereunsure
C.
Mirror-imageTwins
l. 21% of identicalweremirror-imagetwins (accordingto the mother)
2. 23% of themirror-imagetwins weresamehanded
3. 5?% of themirror-imagetwins wereopposite-handed
4. 25% of the mirror-imagetwins wereunsure
D.
of Multiplesand Siblings
Handedness
MultiPles
I.
a. Twin #1 - 56% weteright handed
b. Twin #2 -- 58%wereright handed
c. Triplets(#l' 2 nd 3) - wereright-handed
d. ln 25% of all thesegroups,motherswereunsureof their multiples'
they weretoo young
probablybecause
handedness,
with only 12%beingleft-handed
e. More multipleswereright-handed,
2. Siblings
with only 9 '27obeing left'
of siblingswereright-handed,
a. A high percentage
handed
of siblings#l atrJrl?were left-handedthan subsequent
b. A higherpercentage
slDlmgs
checkedthat they wereunsureof the sibling'shandedness
c. A low percentage
10-95/t4E| 600
Page2
RESEARCHREPORT#12
of Parents
Handedness
of mothersand fatherswere right-handed
1. A high percentage
2. 9% of motherswereleft-handed
3. 13% of tathetswereleft-handed
E.
II.
***++*:trf
Comparisonof Twin Type and Handedness:
A.
Identicaltwirs had the samehandpreferencein 55% of the cases
B.
Fratemaltwins had the samehandpreferencein 48% of the cases
C.
Identicaltripletshad the samehandpreferencein 29% of the cases
D.
Fraternaltripletshad the samehandpreferencein 67% of the cases
E.
42% of identical triplets were unsureof handedness
*+**t
, t 1 . t rl . t t l . i . + x x , l . x . x + * * + ! i ' : i ' ' t * + i ' + + r { ' i ( : F * + ' t * * ' f
* * * * * : L , * * * * * * * * + * t l 'l ' + * * ! t * * : t * i <* * ' * * * * t ( * * * t ' *
CONCLUSION:
of motherswho wereunsureof their multiples'handpreference'
1. Becauseof the high percentage
validity of the statisticsis lessreliable.
tendedto havea slightlyhigheraverageof beingleft-handedthan siblingsor mothers'
Multiples
2.
FatherstendedtohavetheSa'mepercenEgeofleft-handednessasmultiples.
3. The majority of multipleswereright-handed,over 50%'
than fraternals'
4. Identicalshaveslightlyhigher ratesfor beingsame-handed
than
5. This was not the samein triplets.Fraremaltripletshad a higherpercentof being same-handed
identicaltriplets.
In pastliteraturemirror-imagetwins are usually
6. 23% of minor-imagetwins were same-handed.
reported as being oPposite-handed'
were not
and inheritabletraits for handedness
7. Individualfamilieswerenot tracedfor handedness
measured.
*****+*:t*i.+i.**+i.t
*:F + + xxx ++ t(:t * ++ * !t:i. * +x. * ++ + t'* * *'** ***
* 't:* *x* *l' * !it * {"i':* + + 't+ !i'* *+ 'i !* 'i' * *: * i*i' *:l' * x x
articlefor the RESEARCHREPORTcanbe found in the 1990Fall Issueof MoTC's
The accompanying
Notebook.