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AS Level · Information Technology 9626

Modelling

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9.1 · Chapter 9 · AS Level IT · Hodder Education

Modelling

What computer modelling is, why we need it, how spreadsheets make it possible, and the real-world domains where models are used — from financial forecasting to climate change and traffic flow.

🔢 What-If Analysis

⚙️ Characteristics

💡 Why We Need Models

🌍 Uses

The Big Idea: Computer modelling means using a computer to represent real-life situations — financial, scientific, or mathematical — to see what would happen under different conditions without the cost, danger, or time of doing it for real. Spreadsheets are a key tool for this.

9.1.1What-If Analysis

Definition

What-if analysis is asking "what will happen if I change a specific variable?" in a computer model. It explores the consequences of different decisions or scenarios without having to implement them in real life. The model recalculates automatically when any input value is changed — making it possible to explore many scenarios quickly.

A classic example: Morag runs a steel ingot foundry. Her spreadsheet models the weekly profit based on workers' wages, number of ingots produced, selling price, and overheads. She can ask:

→ "What would happen to my profits if I increased workers' pay from $13 to $14?" → change cell B2 to 14 → profit drops from $1,580 to $1,412.

→ "If I also increase the selling price to $12.50, would that make up the difference?" → change the price cell → new profit calculated instantly.

📌 Key distinction: A calculation and a model both process numbers. But in a model, the rules can be changed without rewriting the program. In a basic calculation, the rules are fixed. This flexibility is what makes spreadsheet models so powerful for what-if analysis.

9.1.2Characteristics of Modelling Software

Spreadsheets are particularly well-suited to modelling because of several built-in characteristics that no other common tool provides together in one package:

⚡ Automatic Recalculation

Every formula that uses changed data recalculates instantly. No need to manually re-run the model after each input change.

🔗 Absolute & Relative Referencing

Allows formulas to replicate correctly — incrementing what should change (relative) while keeping fixed values constant (absolute).

🔒 Cell Protection

Prevents inexperienced users from accidentally changing critical cells (e.g. fixed overheads or tax rates). Only senior staff can amend protected values.

🖥️ User Interface Forms

Make it easier to input values into the model — clearly showing where data should be entered, reducing input errors.

⚙️ Macros

Store sequences of keystrokes to automate operations. Useful for running complex comparisons or repeating analytical tasks.

🎨 Conditional Formatting

Automatically highlights cells that meet specific criteria — e.g. turning profit cells green and loss cells red, so changes are visible instantly.

📊 Automatic Graph Updates

Charts and graphs update automatically when underlying data changes — instantly reflecting the new model state without manual rebuilding.

✅ Validation Rules

Reduce data input errors by ensuring only reasonable values can be entered. Prevents costly mistakes (see: 2012 Olympics ticket oversale).

9.1.3The Need for Computer Models

💰

Cost

🧪

🔮

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Modelling

Modelling

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