Metric · Hooked
Viral coefficient (K)
Invites (or shares) per active user multiplied by the share of invites that become activated users. K near zero while users love the product means fans exist but have no path to share.
Plain label: new users each user bringsAlso known as: K-factor, viral coefficient, invite conversion
K under 0.05 while the PMF survey is at or above 40% in some segment is treated as a forced Spread leak [Analyst]. Report its two parts (invites per active user, invite to activation) separately; guard referral programs with referred-user day-30 retention versus organic.
Limits
What we don’t claim
- The Hook Model is a practical design tool, not a validated or complete theory of behavior.Hooked, Introduction
Sources
Hooked · Nir Eyal
Ch.1
Source IDs: HK-MON04
Book content is paraphrased, never quoted at length. Last verified October 24, 2026.
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