Data are from Suddath R.L., et al. (1990). `Anatomical abnormalities
in the brains of monozygotic twins discordant for schizophrenia,' 
New England Journal of Medicine, 322(12):789-793.

Data are volumes in cm^3 of the left hippocampus (measured by
Magnetic Resonance Imaging) in fifteen sets of monozygotic twins 
where one twin is affected by schizophrenia.  

Note that these data ARE NOT THE ORIGINAL MEASUREMENTS, but are 
simulated based on the reported summary statistics.

These data were reproduced (see caveat above) in:

Ramsey and Schafer (1997). The Statistical Sleuth: A course in methods
of data analysis, Duxbury Press.