MODELS & VARIABLES

The building blocks of economics (Page 1)
- Models are central tools in economics; they help analyze and understand economic problems by focusing on essential elements.
Role of models (Page 2)
- A model is a simplification of reality.
- Useful because it is a simplification; complicated models are more realistic but often not useful.
- Models consist of assumptions, variables, and the relationships between those variables.
- In economics, models are often represented as two-dimensional diagrams or systems of equations.

Definition: A model is a simplified representation of reality.
Utility of simplification: It makes analysis feasible and highlights key mechanisms; overly complex models may be harder to interpret and less useful.
Core components: assumptions, variables, and the relationships between the variables.
Common representations in economics: often 2D diagrams or systems of equations.

There are several ways to classify variables:
- Real vs. nominal
- Dependent (endogenous) vs. independent (exogenous)
- Stock vs. flow

This distinction relates to the units used to measure each variable.
Nominal variables: measured in current dollars (nominal values).
Example (nominal): Ontario minimum wage is $15$ per hour.
Real variables: measured in physical quantities (real units).
Example (real): A teaching assistant can grade $5\ \text{test papers per hour}$ .
Significance: Real vs nominal matters for understanding inflation, purchasing power, and physical quantities independent of price level.

Definitions:
- Dependent variable: determined within a particular model (endogenous).
- Independent variable: determined outside of the model (exogenous).
Terminology:
- Also called endogenous (dependent) and exogenous (independent).
Practical note: The distinction becomes clearer as models are used to analyze economic problems.

Time dimension distinction:
- Stock: measured at a particular point in time (a snapshot).
- Flow: measured over a period of time (accumulation over an interval).
Everyday example: water in a bathtub (the amount of water at a moment vs. the inflow/outflow over time).

Diagram/labels from the transcript (Page 7):
- Flow
- Corresponding Stock
- Household saving
- Household wealth
- Government debt
- Investment spending
- Money
Interpretation note:
- The slide presents a layout with the headers "Flow" and "Corresponding Stock" and lists items beneath. It explicitly pairs some flows with corresponding stocks (e.g., Household saving as a flow and Household wealth as its stock), and lists other items (Government debt, Investment spending, Money) as part of the same example section. The exact pairings beyond the two explicit mappings shown in the transcript are not fully stated in the text provided.

Summary definition: A model is a simplification of reality.
In economics: a model is likely a diagram(s) or a set of equations.
A model consists of:
- Variables
- Assumptions about those variables
Ways to classify variables (as highlighted):
- What units we use to measure them (real vs nominal)
- How they are used in the model (endogenous vs exogenous, dependent vs independent)
- How they are measured with respect to time (stock vs flow)

Model: a simplified representation of reality used to analyze economic problems.
Nominal variable: measured in current dollars; example: $15$ per hour (Ontario minimum wage).
Real variable: measured in physical units; example: $5\ \text{test papers per hour}$ .
Endogenous (dependent) variable: determined within the model.
Exogenous (independent) variable: determined outside the model.
Stock variable: value at a point in time.
Flow variable: value over a period of time.
Common representations: 2D diagrams or systems of equations.