A Primer On Graphs

• Pie Chart: A graph commonly used to present the division of a total among parts is a pie chart. Click the [Pie Chart] button to illustrate. This particular pie chart represents the division of national income among different factor payments--wages, interest, rent, and profit. The pie is the total and each slice represents the portion distributed to each category. Pie charts are a handy way to present information, but are not well suited for more involved economic analysis.


• Bar Chart: A graph used to present data for discrete categories is a bar chart. Click the [Bar Chart] button to illustrate. This bar chart indicates the unemployment rate for each of five demographic groups--total population, males, females, whites, and non-whites. A bar chart provides a useful way to compare information about different groups or categories.


• Line Graph: A graph that tends to be most useful in the construction of graphical models and in doing economic analysis is a line graph. Click the [Line Graph] button to illustrate. This particular line graph shows the relation between two variables--price and quantity. Such line graphs are ideally suited for illustrating scientific principles and hypotheses. They can be used to show how one variable (quantity) is affected by changes in another variable (price).

Two Relations

• Positive or Direct: One type of line graph illustrated by clicking the [Positive Relation] button represents a positive or direct relation between two variables, such as price and quantity. With this line, a higher price is related to a larger quantity. Another way of stating this is that the slope of the line is positive. A common positive relation in economics is the market supply curve.


• Negative or Indirect: A second type of line, one that represents a negative or indirect relation between two variables, such as price and quantity, can be seen by clicking the [Negative Relation] button. With this line, a lower price is related to a larger quantity. Another way of stating this is that the slope of the line is negative. A common negative relation in economics is the market demand curve.