1. Definition
   1. measures
      1. nature
         1. degree
            1. changes in quantity demanded
            2. changes in price of good
   2. Enables us to predict whether TR will rise or fall
   3. when price changes since PED tells us which will be bigger
      1. price change
      2. resulting quantity change
2. Topic
   1. Results
      1. Minus
         1. normal good
      2. plus
         1. giffen good
3. Degree of relationahip
   1. The nature of the relationship is revealed by the Sign
   2. 0
      1. perfectly inelastic
   3. <1
      1. inelastic
         1. Change in demand is less then change in price
   4. 1
      1. unit elastic
         1. giffen good
            1. change in demand = change in price
         2. normal good
            1. luxury
   5. >1
      1. elastic
         1. change in demand is greater then change in price
   6. ∞
      1. perfectly elastic
4. Total Cost
   1. Rises
      1. as input
         1. Vice
         2. Versa
5. Nature of relationship
   1. Positive
      1. Variables move in the same direction
   2. Negative
      1. move in opposite directions