A usual metric that works is comparing the number of registrations vs the number of check-ins vs the final number of people attending the event.
Key Metrics
Attendance: Track number of attendees.
Engagement: Measure participation (questions, polls).
Repeat Attendance: Monitor return rates.
New vs. Returning: Analyze attendee mix.
Social Media: Track likes, shares, and mentions.
Website Traffic: Monitor event page visits.
Email Metrics: Measure open and click-through rates.
Feedback Mechanisms
Surveys: Send post-event surveys for immediate feedback.
Testimonials: Collect attendee testimonials.
Social Media Listening: Monitor comments and discussions.
Community Polls: Use quick polls for specific feedback.
Actions
Analyze Trends: Identify patterns over time.
Act on Insights: Implement improvements based on feedback.
Involve Community: Share findings and planned changes with your community.
I use the post-event survey to track if my attendees resonate with the event and the content.
I measure conversion (# of new members added) and also the 'time to conversion' (from invitation to activation of a new member). I also measure member engagement by member referrals (who has referred most members -- my superfan members). Who is logging in daily/weekly/monthly. I also measure repeat event attendees over time.