Design Psychology
Key question
How does design influence actions?
Design plays a role in what people do: whether they sign up, buy, abandon or donate. This often happens without them realising, for example through default settings, sequences or phrasing.
Learning objective: You will recognise common decision-making effects, use them transparently, and formulate testable hypotheses.
Those who shape decisions bear responsibility for them.
7.1 / Two Systems of Thought
We think fast and slow.
In “Thinking, Fast and Slow”, Daniel Kahneman describes two modes of thought. This is a model, not a description of two separate areas of the brain.
SYSTEM 1
Quick
Automatic, effortless, and intuitive. Recognises patterns and usually makes decisions in everyday life.
SYSTEM 2
Slow
Conscious, demanding and deliberative. Needed when something is new, important or difficult.
Most everyday decisions operate in fast mode. Familiar patterns, clear shapes, and simple language support this. Important or high-stakes decisions, however, require space for slow thinking: clear information, opportunities for comparison, and no rush.
Design can either respect or exploit both modes. The question is always whether people are given the time and information they need to make their decision.
Important decisions take time and clear information.
7.2 / Biases & Persuasion
Decisions follow patterns that design can utilise.
Decisions often follow reliable patterns. You'll encounter four of them particularly often in design:
01
Anchoring effect
The first number mentioned influences subsequent judgements. A crossed-out original price makes the offer appear better value.
02
Default effect
Default settings are often kept. In the case of organ donation, consent rates were significantly higher under an opt-out system (Johnson & Goldstein, 2003).
03
Loss aversion
Losses loom larger than equivalent gains. “Don't miss out on…” is often more powerful than “Win…”.
04
Framing
The same information has a different effect depending on how it is phrased: '90% survive' sounds better than '10% die'.
These effects are tendencies and are not equally strong in all people or across all situations. Only use them with genuine information: fabricated scarcity or fake reviews are deceptive.
In 'Influence', Robert Cialdini outlines six principles of persuasion (the 2021 updated edition adds a seventh: Unity, the sense of belonging to the same group). Each of these appears in design through typical patterns:
01
Reciprocity
When people receive something, they want to give something back. In design: free samples, useful content.
02
Consistency
We want to align with earlier commitments. In design: small first steps, progress indicator.
03
Social proof
We follow others. In design: reviews, testimonials.
04
Authority
We trust experts. In design: expert seals, certificates.
05
Likability
We are more likely to say yes to people we like. In design: faces, a personal tone of voice.
06
Scarcity
Rarity creates value. In design: countdowns, limited quantities.
Honesty is crucial: a genuine seal of quality provides guidance, while an invented one deceives. Persuasion thrives on trust; abuse it, and you lose it.
Whoever understands the effects can use them or abuse them.
7.3 / Nudging
A nudge gently guides and leaves you with the choice.
The term nudge originates from Richard Thaler and Cass Sunstein (2008). It refers to the design of the choice environment (choice architecture) that alters people's behaviour in a predictable way without forbidding any options or significantly changing their economic incentives.
Well-known examples include default settings, the order in which options are presented, or a target painted inside a urinal designed to improve aim. The impact of nudges varies in studies and depends on the context.
Good nudges are transparent, serve the interests of users, and are easy to opt out of. When guidance solely benefits the provider or remains concealed, the nudge becomes a dark pattern (see Module 08).
A good nudge helps the individual, not just the provider.
7.4 / Motivation
Behaviour requires a trigger, opportunity, and motivation.
BJ Fogg's behaviour model states that a behaviour occurs when motivation, ability, and a prompt converge. If any of these is missing, the action does not take place. Design can increase ability by simplifying steps, and by placing prompts appropriately.
Habits often follow a loop of trigger, action, and reward. Nir Eyal derived the Hook Model from this. It can be used productively, for instance in learning apps, but also exploited, such as in infinite feeds.
Gamification uses game elements such as points, badges, or progress bars. It can be motivating, but it has its limitations: external rewards can crowd out intrinsic motivation (Deci & Ryan: people stay engaged when they experience autonomy, competence, and relatedness, not because of points), and streaks or leaderboards can create pressure. Always ask yourself whether it genuinely supports the user's goal.
First make the action easy, then motivate.
Exercise
Apply, evaluate, transfer
Task: Design a decision-making scenario with two variants, for example a newsletter sign-up or a donation form.
STEP 1
Formulate a hypothesis using the template: If I change X, then Y will happen, because Z.
STEP 2
Only change one thing (for example, the default setting, order, or phrasing).
STEP 3
Determine how you will tell whether the hypothesis is correct (observation criterion).
STEP 4
Think about how you would test the variations and how many people you would ask.
Evaluation: Which variant is more transparent for users? Would you publish both variants? Where is the line between helping and influencing?