1. Impact of Change in Income
Here we want to consider the change consumers will make if they experience a change in income.

2. change in income.
Note that the budget line is a summary of the baskets of goods that a consumer can buy. The consumer ultimately picks the basket that is able to be purchased and gives the individual the most satisfaction or happiness.
For the next few slides let’s just think about the budget line and not about consumer utility maximization.

3. change in income - budget changey
Remember on the budget line we are measuring the amount of x and y the consumer can buy given their income and given the fact that prices must be paid. y1 x x1
I have illustrated one basket the consumer can buy. With the price of x = Px and the price of y = Py the consumer here could buy x1, y1.

4. change in income - budget changey
There are many ways to think about how the budget line would change given an income change, but one way to think about it would be to pick a given amount of x, say x1. Before the income y2 y1 x x1
change say that once x1 is bought that leaves only y1 of y. Now if there is an income increase, after x1 is bought that would leave more money to spend on y and thus y2 could be bought.

5. change in income - budget change
From the previous screen we can see more y can be bought if there is more income available, but how much more depends on the prices of x and y and it depends on the income change.
But, as income rises more y can be bought, given an amount of x is bought. Thus the budget line shifts out in a parallel fashion if income grows and by a similar logic shifts in parallel if there is an income decline.

6. change in income - optimal point change
Now that we know how the budget changes given an income change, let’s see how the consumer optimum changes(given that taste and preferences do not change).

7. change in income - optimal point changey
Say the consumer starts out at point a - x1, y1 gives maximum satisfaction. Note I have extended a line above point x1.
Now with more income the budget line shifts out. The consumer will end up either y1 a x x1
to the right or the left of the dashed line. If the consumer ends up to the right, more x is wanted with more income. If the consumer ends up to the left of the dashed line then less x is wanted when more income is obtained.

8. change in income - optimal point change
A normal good is one where that as the consumer gets more (less) income more (less)of the product is demanded.
An inferior good is one where as the consumer gets more (less) income less (more) of the product is demanded.
An Engel curve is a graph that provides a summary of what happens to the demand for a product as income levels change.

9. Engel curve - normal goody x x2 x1 y1 a x
income
I1 I2
x1 x2
In the right hand picture we can see an income increase and from the left graph we take the new x, x2, and draw it in with the new income level. The Engel curve for a normal good is upward sloping. What about for an inferior good?

10. y
X is an inferior good. x