AS Level IT (9626) Study Notes: Topic 9 - Modelling
Welcome to one of the most practical and exciting topics in AS Level IT: Modelling!
This chapter moves beyond simple calculations and asks the big question: "What if?"
You will learn how IT systems, especially spreadsheets, can create simplified virtual versions of complex real-world systems. This allows businesses, scientists, and governments to test scenarios safely, predict outcomes, and make better decisions.
Don't worry if this sounds complicated! A model is just a tool—like a fancy calculator—that helps us see the future based on our current data.
9.1 Modelling and Simulations
What Exactly is a Model in IT?
A computer model is a simplified mathematical representation of a real-world process, system, or object.
It uses algorithms (formulas and rules) and data to imitate reality.
Analogy: Think of a car model made of LEGO. It’s not a real car, but it shows you the basic structure and relationship between the wheels and the body. A computer model is the same, but instead of plastic blocks, it uses data and formulas.
Key Modelling Techniques: What-if Analysis and Goal Seek
The primary reason we build models is to test out different situations without actually having to risk real money, time, or safety.
1. What-if Analysis
This is the most common use of a model. It involves changing the input data (variables) to predict how the output results will change.
Purpose:
• Predict the result of changing data.
• Change data to model different scenarios.
Example: A company selling phones has a spreadsheet model for profit. They use What-if Analysis to change the price of the phone (input) from $500 to $450 to see if the reduction leads to enough extra sales volume to increase the overall profit (output).
2. Goal Seek
Goal Seek works in reverse of What-if Analysis. Instead of changing an input and seeing the output, you start with the desired output (the goal) and ask the system to calculate the required input needed to achieve that goal.
Example: You want to earn exactly $100,000 profit next year (the goal). You use Goal Seek to determine exactly how many units (input) you must sell to hit that target, assuming your costs stay the same.
Quick Review Box: What-if vs. Goal Seek
• What-if: I change A, what happens to B? (Forward calculation)
• Goal Seek: I need B to be this value, what must A be? (Backward calculation)
Common Uses of Modelling
Models are used extensively across nearly every sector to predict and manage complex situations.
The syllabus requires knowledge of these key uses:
• Financial forecasting: Predicting future income, expenditure, and profitability for businesses or governments. (Essential for budgeting.)
• Population growth: Calculating how quickly a population will change based on birth rates, death rates, and migration. (Important for city planning and resource allocation.)
• Climate change: Using massive, complex models to simulate atmospheric, oceanic, and biological systems over decades.
• Weather systems: Predicting rainfall, temperature, and wind patterns. (Highly dependent on collecting vast amounts of data.)
• Queue management: Designing optimal flow in banks, airports, or supermarkets by modelling customer arrival times and service speed to reduce waiting times.
• Traffic flow: Simulating how new road networks, traffic lights, or roundabout designs will affect congestion before they are built.
• Construction: Modelling the stress on building structures (e.g., bridges, skyscrapers) under different conditions (e.g., wind, earthquake stress).
Characteristics and Effectiveness of Computer Models
Why do we need computer models instead of calculating everything by hand?
The Need for Computer Models
Computer models are necessary because real-world systems often involve:
• Very large amounts of data: A weather model processes trillions of data points.
• Complex variables and relationships: Many factors interact simultaneously (e.g., in climate change, temperature affects rainfall, which affects vegetation, which affects temperature...)
• Speed: They can run calculations much faster than humans.
• Safety/Cost: They allow testing scenarios that would be too dangerous or expensive in real life.
Characteristics of Modelling Software
Good modelling software (or a good modelling spreadsheet) usually features:
• The ability to define variables (inputs) and parameters (fixed constants, e.g., speed of light).
• Sophisticated built-in mathematical and logical functions.
• Tools for data visualisation (charts and graphs) to interpret results easily.
• Built-in tools like What-if Analysis and Goal Seek.
Effectiveness of Spreadsheet Models
Spreadsheets are frequently used for basic modelling tasks (especially financial and resource models).
Advantages:
• They are readily available, easy to understand, and relatively simple to program with formulas.
• They are excellent for handling numerical data and relationships (e.g., budgets).
Limitation (A Crucial Point!):
The effectiveness of any model, particularly a spreadsheet model, relies entirely on the quality of its inputs and formulas. This is summarised by the principle: Garbage In, Garbage Out (GIGO). If your formulas are wrong, or your initial data is flawed, the prediction will be useless.
Simulations: Bringing Models to Life
While a model is the static structure (the rules and formulas), a simulation is the act of running that model over time to observe its behaviour.
A simulation attempts to imitate the physical processes of the real world.
Use of a Model to Create and Run Simulations (High-Risk/Complex Scenarios):
• Pilot training / learning to drive a car: Simulators provide a realistic, safe, and repeatable environment to practice critical skills without damaging expensive equipment or risking lives.
• Natural disaster planning: Emergency services can simulate scenarios like earthquakes or floods to test evacuation routes, resource deployment, and communication breakdowns.
• Nuclear science research: Experiments involving radioactive materials or particle physics are often modelled digitally first, as real-world testing is extremely hazardous and costly.
Did you know? Modern air traffic control systems use simulations heavily to train new controllers. They can throw dozens of simultaneous emergencies at trainees without a single real plane being affected.
Key Takeaway
Modelling and simulation are essential IT tools used to replicate complex reality in a controlled, safe, and timely environment. Master What-if analysis (changing inputs) and Goal Seek (finding inputs) and remember that the model is only as good as the data and rules you put into it!