Discuss why the link between smoking and lung cancer is considered a causal relationship and why the link between living near power lines and cancer...

Discuss why the link between smoking and lung cancer is considered a causal relationship and why the link between living near power lines and cancer is considered an association. Use the information from the following two websites to support your answer. Make sure to explain what is necessary to establish causation.

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Epidemiology.html

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/MagneticFields.html