Scale / Parametric vs. Nonparametric tests

http://en.wikipedia.org/wiki/Scale_(social_sciences)

http://changingminds.org/explanations/research/analysis/parametric_non-parametric.htm
http://www.mymarketresearchmethods.com/types-of-data-nominal-ordinal-interval-ratio/ 
http://changingminds.org/explanations/research/analysis/parametric_non-parametric.htm