How do I measure the impact of frequency on engagement and unsubscribes?

Frequency impact measurement requires both per-email and cumulative views:

Per-email metrics:

Open rate per email (does it decline with higher frequency?). Click rate per email. Revenue per email.

Cumulative metrics over time:

Total opens over the test period. Total clicks and conversions. Total revenue generated.

Attrition metrics:

Unsubscribe rate per email. Cumulative unsubscribes over time. Complaint rates. List decay rate.

Long-term value:

Subscriber lifetime value by frequency group. Retention rates over extended periods.

The tradeoff analysis: Higher frequency may generate more total revenue short-term but cause faster list decay. Model the long-term economics.

Frequency optimization balances short-term gain against long-term sustainability. Measure both to make informed decisions.