Concept · Platforms

Cross-side network effects

Participation on one side of a platform changes the value received by another side, so growth and pricing must be analyzed together.

Participation across two distinct sides changes the value of exchange.

A cross-side network effect occurs when participation or useful activity in one group changes value for another group. Identify both groups and the mechanism. A seller registration and a buyer outcome are different observations.

In one sentence

A cross-side network effect occurs when the number or quality of participants on one side of a platform changes the value that participants on another side receive.

The decision is which participation will improve a relevant match, capability or acceptance. More supply can help when it meets the task’s conditions, yet make search harder when it is unsuitable. Location, timing and quality can determine the direction.

The effect need not be symmetric. Additional buyers may improve a seller’s opportunity, while additional sellers increase competition for existing sellers. Keep cross-side benefits separate from same-side rivalry and the platform’s own revenue.

Cross-side mechanisms

Name the participating groups and the value that flows between them.

Matching

More active participants on one side improve the chance of finding a suitable counterpart.

Reach and access

One group values access to the customers, content, or inventory supplied by another.

Shared transaction system

Participation on both sides increases acceptance or usefulness of a common payment or exchange layer.

A continuum, not a switch

The effect is stronger when one side’s activity measurably improves another side’s available matches, reach, acceptance, or outcomes.

LowSides act independentlyHighParticipation is interdependent

“Count useful matches, not just participants.”

Why it matters

The CMA’s platform guidance distinguishes effects across participant groups and recognizes that they need not work in both directions. The operating question is therefore specific: whose participation changes which other group’s task? The examples below document actual offer and support choices; their disclosures do not measure the incremental effect of another participant.

Trace the added participant to the available outcome. A listing can be technically present but unavailable for the desired dates. A developer can publish an application that users do not need. Count the activity that affects feasible choices rather than substitute membership for value.

Demand growth, promotion and a change in quality can explain transaction growth alongside participation. Examine a defined market and period, including what each group would do through another route. The platform label cannot supply that counterfactual.

Real-world examples

The same concept shows up in different ways across industries.

AirbnbRelevant supply needs an operating capability

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Airbnb’s FY2024 filing describes co-host assistance and risks concerning supply, quality and participation. The actual support choice can help a host operate a listing; a guest benefits only if that capability produces suitable availability for the guest’s request. A more capable host and a completed guest booking are distinct events. The cross-group mechanism must connect them rather than assume the result from program enrollment. The manager’s choice is which supply activity is missing and whether the response creates a usable option. Assistance may be appropriate where a host cannot perform needed work. Better matching may matter where suitable listings already exist. The filing does not compare those alternatives or isolate the incremental effect of another usable listing in a local market. Demand growth, promotion, price and quality can also change bookings. Follow the host capability through availability to the guest task, while separately examining any effect on competing hosts. The disclosure supports an operating design and its risks, not a symmetrical or automatically reinforcing participation effect.

MicrosoftContent and access connect groups

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Microsoft describes Xbox content, certified applications and developer or partner access. This identifies contributors and users in a combined offer. It does not show that every added application benefits users or quantify a contributor’s economic return.

When it breaks

For a hypothetical marketplace, low-quality sellers increase the listing count while buyers spend more effort searching. A participation objective can move opposite to the customer outcome. Track relevant availability and completed tasks.

An apparent cross-side benefit can be funded by temporary support. Include the operating burden and examine whether participants continue when that support changes. Positive activity under an intervention does not establish a self-sustaining effect.

Key takeaways

01
Name both sides and the value transfer between them.
02
Measure active, relevant matches rather than registrations alone.
03
Treat subsidy, local density, quality, and multi-homing as separate conditions.

Sources

Airbnb FY2024 Form 10-K: Co-Host Network introduction · Airbnb / SEC. Item 1, Our Platform / Our Platform for Hosts, printed p. 4, paragraph beginning “During 2024, we introduced Co-Host Network”; Our Long-Term Growth Strategy immediately above
Airbnb FY2024 Form 10-K: host quality and competition · Airbnb / SEC. Item 1A, Revenue and Growth Risks, printed p. 8: heading beginning “If we fail to retain or add hosts and guests”, paragraphs on listing quality, host cross-listing, initiative adoption and community-support cost; competition heading beginning “The business and industry in which we participate”, printed pp. 13–14
Microsoft 2024 Annual Report · Microsoft. Business, More Personal Computing, Gaming: first- and third-party content; certified applications; developer/partner access; availability of games
Merger Assessment Guidelines: platforms and network effects · Competition and Markets Authority. Merger Assessment Guidelines, updated September 3, 2026, “Two-sided platforms and network effects” section; passage addresses indirect network effects between distinct groups and that effects may be asymmetric.