Graphs in Economics: Foundations for Microeconomic Analysis

Graphs in Economics

Introduction to Economic Graphs

Graphs are essential tools in microeconomics for visualizing relationships between economic variables. They help economists and students interpret data, identify patterns, and analyze economic models.

• Graphs reveal relationships between variables such as price, quantity, income, and expenditure.

• Axes: The vertical axis is the y-axis, and the horizontal axis is the x-axis. The intersection is called the origin.

• Two-variable graphs use perpendicular scale lines to plot data points.

Plotting Data Points

To plot a point on a graph, both the x-value and y-value are required. For example, to plot a point representing 5,959 meters above sea level at 10°C:

• Point A: x-value is 10°C.

• Point B: y-value is 5,959 meters.

• Point C: Represents the combination of these values.

Economic Variables and Graphs

Economists measure variables that describe what, how, and for whom goods and services are produced. Common variables include quantities produced and prices.

• Graphs can show, for example, the number of movie tickets sold and their average price in a given year.

• Example: In 2023, 61 million movie tickets were bought at $9.17 each.

Scatter Diagrams

A scatter diagram plots the value of one variable against another for multiple observations. It is used to reveal whether a relationship exists between two variables.

• Example: Comparing production budgets and worldwide box office revenues for movies.

• Scatter diagrams can show patterns, such as whether higher budgets lead to higher revenues.

Movie	Production Budget (millions)	Worldwide Box Office (millions)
Avatar: The Way of Water	460	2,131
Thor: Love and Thunder	250	761
Spider-Man: No Way Home	200	1,910
Doctor Strange in the Multiverse of Madness	200	952
The Batman	200	770
Fantastic Beasts: The Secrets of Dumbledore	200	405
Black Adam	200	391
Lightyear	200	219
The Matrix Resurrections	190	159

Additional info: The pattern of points in the scatter diagram may not always show a clear relationship; for example, higher budgets do not always result in higher box office revenues.

Types of Relationships in Economic Data

Graphs in economics can illustrate several types of relationships between variables:

• Positive (Direct) Relationship: Both variables move in the same direction. Shown by an upward-sloping line. If the relationship is a straight line, it is called linear.

• Negative (Inverse) Relationship: Variables move in opposite directions. Shown by a downward-sloping line.

• Maximum or Minimum: The relationship is positive over part of the range and negative over another, resulting in a curve with a peak (maximum) or trough (minimum).

• Unrelated Variables: No discernible pattern; the graph may show a flat line.

Examples of Relationships

• Income and Expenditure: As income increases, expenditure also increases, indicating a close positive relationship.

• Inflation and Unemployment: No clear relationship; points are scattered without a pattern.

Slope of a Relationship

The slope measures the rate at which one variable changes in relation to another. It is calculated as:

• Formula: $\text{Slope} = \frac{\Delta y}{\Delta x}$

• $\Delta y$ is the change in the y-variable; $\Delta x$ is the change in the x-variable.

• Positive slope: Upward-sloping line.

• Negative slope: Downward-sloping line.

Slope of a Straight Line

• The slope is constant along a straight line.

• Calculated as "rise over run."

Slope of a Curved Line

• The slope varies at different points along the curve.

• Slope at a point: Equal to the slope of the tangent line at that point.

• Average slope across an arc: Equal to the slope of the straight line joining the endpoints of the arc.

Graphing Relationships Among More Than Two Variables

When more than two variables are involved, economists use the ceteris paribus assumption, meaning "all other relevant things remain the same," to isolate the relationship between two variables.

• Example: The quantity of ice cream consumed at different prices as temperature varies.

Price ($/scoop)	Ice Cream Consumption (litres per day) at 21°C	Ice Cream Consumption (litres per day) at 32°C
2.00	15	30
2.25	13	26
2.50	12	24
2.75	10	20
3.00	7	14
3.25	5	10

• Holding temperature constant at 21°C, changes in price result in movement along the blue curve.

• Holding temperature constant at 32°C, changes in price result in movement along the red curve.

• When temperature rises from 21°C to 32°C, the curve shifts rightward, indicating increased consumption at each price.

Summary Table: Types of Relationships in Economic Graphs

Type of Relationship	Description	Graphical Representation
Positive (Direct)	Variables move in same direction	Upward-sloping line
Negative (Inverse)	Variables move in opposite directions	Downward-sloping line
Maximum/Minimum	Relationship changes direction	Curve with peak or trough
Unrelated	No pattern	Flat line

Key Terms

• Scatter diagram: Graph showing values of two variables for multiple observations.

• Slope: Rate of change between two variables, calculated as $\frac{\Delta y}{\Delta x}$.

• Ceteris paribus: Assumption that all other variables are held constant.

• Linear relationship: Relationship shown by a straight line.

• Nonlinear relationship: Relationship shown by a curve.

Applications in Microeconomics

• Graphs are used to analyze demand and supply, consumer behavior, production costs, and market equilibrium.

• Understanding how to interpret and construct graphs is foundational for further study in microeconomics.

Additional info: These notes provide foundational skills for interpreting economic data and models, which are essential for topics such as demand and supply analysis, elasticity, and market structures in microeconomics.