An introduction to the least squares regression line in simple linear regression.
The pain-empathy data is estimated from a figure given in:
Singer et al. (2004). Empathy for pain involves the affective but not sensory components of pain. Science, 303:1157--1162.
The Janka hardness-density data is found in:
Hand, D.J., Daly, F. , Lunn, A.D., McConway, K., and Ostrowski, E., editors (1994). The Handbook of Small Data Sets. Chapman & Hall, London.
Original source: Williams, E.J. (1959). Regression Analysis. John Wiley & Sons, New York. Page 43, Table 3.7.