Almost every algorithm you will be shown is built from four things. Learn them as parts you can spot inside a description, not as definitions to recite.
- Instructions
- The steps themselves — do this, then do that.
- Variables
- Named places that hold a value while the algorithm runs, so it can remember something between steps.
- Conditionals
- Do something only IF something is true. This is where decisions enter.
- Loops
- Repeat the same steps until a condition is met. This is what makes an algorithm scale.
One algorithm that counts unread messages, with each part highlighted in turn.
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Of the four, the conditional is the one exam questions keep returning to, because a single threshold decides who is treated one way and who is treated another.
| The rule | Who it helps | Who it quietly removes |
|---|---|---|
| IF score is above 35, continue | Anyone above the line | Anyone at 35, whatever else is true of them |
| IF address is inside the city | Local applicants | People who moved recently, and commuters |
| IF the gap in work is under a year | Continuous careers | Carers, and anyone who was ill |
Why a threshold is not neutral: A line has to be drawn somewhere, and wherever it is drawn somebody sits just on the wrong side of it. The system cannot see that person at all, because to the rest of the algorithm they no longer exist.
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The loop is what turns a rule into a policy. The same four lines that sort ten applications sort ten million, at no extra cost and with no extra thought.
Real-world examples you can name
Amazon's scrapped CV-screening tool — reported October 2018
An experimental hiring tool was trained on a decade of CVs submitted to the company, most of them from men. It learned to downgrade CVs containing the word 'women's' and graduates of two women's colleges. The project was abandoned.
Who it affected: Women applying for technical roles, and every organization that assumed historical data was neutral.
Platform work and employment status — UK Supreme Court ruling on Uber drivers February 2021; EU platform work directive adopted 2024
Work is allocated by an app rather than a manager. The UK Supreme Court held that Uber drivers are workers entitled to minimum wage and holiday pay, and the EU has since legislated a presumption of employment where a platform controls the work.
Who it affected: Couriers and drivers, and companies whose model assumed self-employment.
The concept doing work here: Power. Writing a rule once used to affect one decision. Writing it inside a loop applies it to everyone, which is a different kind of power from the one a manager had.
How this is tested — you have to name the parts inside a described system and explain what one of them does to people. It comes up two ways:
Paper 1 — structured question
- Part a: identify components of an algorithm
- Part b: explain how a condition can exclude suitable people
Paper 2 — source-based question
- Q2: explain a rule a source describes
- Q4: synthesise sources on an automated decision
The trap: describing the software: A question about components wants instructions, variables, conditionals and loops — not the app, the database or the interface.
Explain two reasons why using a single score threshold in a decision tree may reject suitable people.
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