The 20 brain volumes (cm3) from Data Set 8 “IQ and Brain Size” in Appendix B vary from a low of 963 cm3 to a high of 1439 cm3. Use the range rule of thumb to estimate the standard deviation s and compare the result to the exact standard deviation of 124.9 cm3.

Data Set 8: IQ and Brain Size 

Data are from 20 monozygotic (identical) twins (first five rows shown here). PAIR identifies the set of twins, SEX is the gender of the subject (1 = male, 2 = female), ORDER is the birth order, IQ is measured full IQ score, VOL is total brain volume (cm3), AREA is total brain surface area (cm2), CCSA is corpus callosum (fissure connecting left and right cerebral hemispheres) surface area (cm2), CIRC is head circumference (cm), and WT is body weight (kg). 

Data provided by M. J. Tramo, W. C. Loftus, T. A. Stukel, J. B. Weaver, M. S. Gazziniga. See “Brain Size, Head Size, and IQ in Monozygotic Twins,” Neurology, Vol. 50.