Download Geo-point Graphs: An Alternative to Marshallian Cross Diagrams

Geo-point Graphs: An Alternative
to Marshallian Cross Diagrams
November 8, 2012
Economics Teaching Conference
Orlando, FL
The Marshallian Cross
• ...the law of demand...is the single most
powerful proposition in all of economics...[it]
has the capacity to explain an incredibly
diverse range of human behaviors...The great
explanatory power of the law of demand is
almost matched by that of the law of supply...
(Miller, Benjamin and North, p. 27)
Price
$20
Supply
$15
$10
$5
0
Demand
5
10
15
20
Quantity
Demand and Supply Line Graphs
• Simplify the complexities of the price system
• But line graphs are challenging for students
Student/Instructor Personality Types
• Using Meyers-Briggs Type Indicator (MBTI)
• Roanoke College Freshman (F’90) – less than
5% were INTJ – many instructors (including
me) are INTJ: “Introverted Intuition with
Extraverted Thinking”
• A plurality of students were ENFP:
“Extraverted Intuition with Introverted
Feeling”
INTJ
• “Usually have original minds and great drive for their
own ideas. Have a fine power to organize a task and
carry it through without help in areas that appeal to
them. Are skeptical, critical, independent,
determined, and often stubborn. Tend to be serious
and to set high standards. Prefer challenging
teachers. Don’t readily follow fads.” (And love
graphs!)
ENFP
• “Are warmly enthusiastic, ingenious, and imaginative.
Are able to do almost anything that interests them.
Are quick with a solution for any difficulty. Are
interested in people and skillful in handling them and
their problems. Often rely on their ability to
improvise instead of preparing to advance. Dislike
inspired routine and attention to detail.” (And hate
graphs!)
Does it Matter?
• No one is recommending getting rid of line
graphs
• But an alternative, complementary approach
has value:
• 1. For K-12 instructors & Students
• 2. For instructors and students who are not
INTJ
• 3. For empirical market studies
1. K-12 Instructors and Students
• 49 states have economics standards – many
require knowledge of markets in middle
school
• PA - Describe the interaction of consumers and
producers of goods and services in the state
and national economy (6th grade)
• To be effective – K-8, not just HS - teachers
must teach demand and supply
2. Non INTJ Students
• “Chalk and Talk”- still dominant among
economics Instructors (Watts/Becker surveys)
• “If we want to increase learning in economics, then we
need to devise ways of presenting course material that
are accessible to all students regardless of how they
receive and process information. At a minimum, this
suggests the need for a variety of classroom pedagogies
and a better understanding of the role of personality
temperament in learning and teaching.”
(Ziegert)
3. What’s Wrong with This Example?
Chevrolet Silverado
PU
November 2009
June 2012
Price (MSRP)
Quantity Sold
$19,375
$22,195
31,754
33,566
In Real Markets We “see” actual, not
hypothetical prices
• Line graphs represent a “convenient fiction”
• 1. They imply continuity.
• 2. They do not distinguish actual from
hypothetical prices.
Price
Shortage - only the circle and
square in black are “seen”
$20
$15
$10
$5
0
5
10
15
20
Quantity
Price
$20
$15
$10
$5
0
5
10
15
20
Quantity
Price
$20
Equilibrium price is
the market price
$15
$10
$5
0
5
10
15
20
Quantity
Changes in Demand and Supply
• On the following slide:
• I – increase in demand moves equilibrium
point into this quadrant
• II – increase in supply moves equilibrium into
this quadrant
• III – decease in demand moves equilibrium
into this quadrant
• IV – decrease in supply moves equilibrium into
this quadrant
Price
$20
$15
IV
I
III
II
$10
$5
0
5
10
15
20
Quantity