"Relationship between IQ and Brain Size Summary: Monozygotic twins share numerous physical, psychological, and pathological traits. Recent advances in in vivo brain image acquisition and analysis have made it possible to determine quantitatively whether: 1) twins share neuroanatomical traits; and 2) neuroanatomical measures correlate with brain size. Using magnetic resonance imaging and computer-based image analysis techniques, measurements of the volume of the forebrain, the surface area of the cerebral cortex and the mid-sagittal area of the corpus callosum were obtained in 10 pairs of monozygotic twins. Head circumference, body weight, and Full-Scale IQ were also measured. Analyses of variance were carried out using genotype, birth order, and sex, as between-subject factors. Pearson correlation coefficients were computed to assess the interrelationships between brain measures, head circumference, and IQ. Effects of genotype (but not of birth order) were found for total forebrain volume, total cortical surface area, and callosal area. Consistent with previous twin studies, highly significant effects of genotype but not birth order were also found for head circumference, body weight, and Full-Scale IQ. The significant effect of genotype on all measures was not attributable to sex differences across unrelated twin pairs. Significant correlations were observed between forebrain volume, cortical surface area, and callosal area as well as between each brain measure and head circumference. No correlation between IQ and any other measure was found. Monozygotic twins share similarities in forebrain volume, cortical surface area, and callosal area. Brain measures are highly correlated with one another and with head circumference, but none is correlated with IQ. Authorization: Contact Authors Reference: Tramo MJ, Loftus WC, Green RL, Stukel TA, Weaver JB, Gazzaniga MS. Brain Size, Head Size, and IQ in Monozygotic Twins. Neurology 1998; 50:1246-1252. Description: This datafile contains 20 observations (10 pairs of twins) on 9 variables. This data set can be used to demonstrate simple linear regression and correlation. Variable Names in order from left to right: CCMIDSA: Corpus Collasum Surface Area (cm2) FIQ: Full-Scale IQ HC: Head Circumference (cm) ORDER: Birth Order PAIR: Pair ID (Genotype) SEX: Sex (1=Male 2=Female) TOTSA: Total Surface Area (cm2) TOTVOL: Total Brain Volume (cm3) WEIGHT: Body Weight (kg) Therese Stukel Dartmouth Hitchcock Medical Center One Medical Center Dr. Lebanon, NH 03756 e-mail: stukel@dartmouth.edu Information about the dataset CLASSTYPE: numeric CLASSINDEX: 2 " "0" "iq_brain_size" "Female" "Female" "Female" "Female" "Female" "Female" "Female" "Female" "Female" "Female" "Male" "Male" "Male" "Male" "Male" "Male" "Male" "Male" "Male" "Male" 6.08 5.73 6.22 5.8 7.99 8.42 7.44 6.84 6.48 6.43 7.99 8.76 6.32 6.32 7.6 7.62 6.03 6.59 7.52 7.67 54.7 54.2 53 52.9 57.8 56.9 56.6 55.3 53.1 54.8 57.2 57.2 57.2 57.2 55.8 57.2 57.2 56.5 59.2 58.5 1913.88 1684.89 1902.36 1860.24 2264.25 2216.4 1866.99 1850.64 1743.04 1709.3 1689.6 1806.31 2136.37 2018.92 1966.81 2154.67 1767.56 1827.92 1773.83 1971.63 57.607 58.968 64.184 58.514 63.958 61.69 133.358 107.503 62.143 83.009 61.236 61.236 83.916 79.38 97.524 99.792 81.648 88.452 79.38 72.576 96 89 87 87 101 103 103 96 127 126 101 96 93 88 94 85 97 114 113 124 1 2 1 2 1 2 1 2 1 2 2 1 2 1 2 1 1 2 2 1 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 1005 963 1035 1027 1281 1272 1051 1079 1034 1070 1173 1079 1067 1104 1347 1439 1029 1100 1204 1160 "CCMIDSA" "FIQ" "HC" "ORDER" "PAIR" "SEX" "TOTSA" "TOTVOL" "WEIGHT" "double0" "int1" "double2" "int3" "SEX" "double4" "int5" "double6" "numeric" "numeric" "numeric" "nominal:1,2" "nominal:1,2,3,4,5,6,7,8,9,10" "nominal:Female,Male" "numeric" "numeric" "numeric"