The psychology behind ecommerce, with the evidence attached.

104 principles that shape how people shop online, each one mapped to the pages where it matters, linked to the research behind it, and rated on how well that research has held up.

Often looked up:Social proof Anchoring Scarcity Default effect

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Loss & ScarcityEvidence: Contested

Urgency (time limits)

Deadlines can speed up decisions, and restrictions can signal that a deal is good.

Applies to Product, Homepage, Cart, Checkout

What the research found

Online, time-limited promotions often did no better than the same offer with no deadline.

Key research

Hmurovic, Lamberton & Goldsmith (2023) J. Marketing Research

Barton, Zlatevska & Oppewal (2022) J. Retailing, meta-analysis

104principles, each summarised in plain English

407research citations, each linked to its source

8areas of a site, from homepage to post-purchase

9kinds of psychology, from social influence to pricing

Browse by page

Start with the page you’re working on.

Follow the customer's route through the site and see which principles are at work at each step.

01HomepageThe first impression, and the way in.46 principles 02CategoryWhere shoppers browse and narrow down.43 principles 03SearchWhere shoppers say what they want.24 principles 04ProductWhere the decision is made.73 principles 05CartWhere the order takes shape.37 principles 06CheckoutWhere the purchase is completed.39 principles 07Post-purchaseEverything after the order is placed.29 principles

SitewideNavigation, speed, layout and trust, on every page. 38 principles

Your CPI Rating

See how your own pages score.

We check your site page by page against all 104 principles and give each page, and the site as a whole, a CPI Rating out of 100. It’s free, assessed by a person, and with you within five working days.

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Exampleyourbrand.co.uk CPI RatingSolid, with clear gaps in the basket Homepage71Category58Product66Cart44Checkout62

Browse by psychology

Or by the kind of thinking it relies on.

Nine groups, each drawing on a different part of how people decide.

Social influenceWhat other people do, say and recommend.9

Loss and scarcityThe pull of what might be missed or lost.6

Choice architectureHow options are arranged, ordered and pre-selected.17

Pricing and value perceptionHow a price is judged, not only what it is.12

Cognitive load and fluencyHow much effort a page asks of the shopper.11

Attention and perceptionWhat gets noticed, and what gets skipped.12

Motivation and commitmentWhat keeps people moving towards a goal.15

Trust and risk reductionWhat makes buying from a stranger feel safe.9

Emotion and memoryWhat people feel, and what they remember afterwards.13

How we rate the evidence

Only 31 of 104 principles earn our strongest rating.

Every entry is checked against the published research, including the replications and meta-analyses that came after the famous first study, and where a well-known tactic turns out weaker than its reputation, the entry says so. Of those 31, 15 have also been tested on real shoppers.

31Strong Replicated many times, or backed by a meta-analysis. See all 31 58Moderate Solid studies, but dependent on context or tested mainly in the lab. See all 58 7Contested Failed replications, or an effect that is weak or conditional. See all 7 8Framework A useful way of thinking, not a single measured effect. See all 8

Read how entries are researched and rated

Three things the research changed our minds on

ContestedCountdown timersOnline, a time-limited offer often does no better than the same offer with no deadline, unless the deadline has a believable outside reason.Read the entry ContestedThe decoy optionThe effect holds when options are compared on numbers alone, and largely disappears once shoppers can see photos or the product itself.Read the entry Often misreadHick's lawIt doesn’t say fewer options are always better; it says each extra option adds less decision time than the one before.Read the entry

From the database

Three well-supported places to start.

See all 104 principles

Social influenceStrong Social proofWhen unsure, people look to what others have done and follow it. Applies to Product, Homepage, Category and 2 more Read the entry Choice architectureStrong Default effectPeople tend to stick with whatever is pre-selected. Applies to Checkout, Product, Cart Read the entry Emotion and memoryStrong Expectation-disconfirmationSatisfaction depends on performance relative to what was promised, so beating a modest promise satisfies more than missing an ambitious one. Applies to Post-purchase, Sitewide, Product and 2 more Read the entry

Start with the page you’re working on.

See how your own pages score.

Or by the kind of thinking it relies on.

Three things the research changed our minds on

Three well-supported places to start.

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