Subscriber numbers
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This is the number of emails you send out with each issue. You need to follow four numbers:
- total number of email addresses.
- change in total number of addresses over a fixed time period.
- number of new addresses added in that time period.
- number of addresses removed in that time period.
You can fix the time period to match your needs. If you make it equivalent to your publication frequency, then you can track issue-to-issue changes.
Normally, it's fair to think of the total number of addresses as equivalent to the total number of subscribers. However, some subscribers may be signed up under more than one address, some addresses may be dud, and some emails may be read by more than one person.
So it's near impossible to tell how large your true theoretical readership is.
The other three numbers tell you about the dynamics of your subscription base. It's not enough to know if your subscriber base is growing or shrinking. You need to know the source of this growth or loss. Consider two newsletters, A and B:
Subscribers Day 1
Newsletter A: 10,000
Newsletter B: 10,000
Subscribers Day 60
A: 11,000
B: 11,000
Addresses added in this period
A: 1000
B: 10,000
Addresses removed in this period
A: 0
B: 9,000
Both newsletters have grown by 1000 subscribers in the 60 day period. But newsletter A has lost no subscribers, whereas newsletter B has lost 9,000. They have the same net subscriber growth, but newsletter A is obviously working better than newsletter B. Or is it?
You'd also need to consider the source of the new subscribers to newsletter B. Suppose they all signed up with false expectations? Maybe it's newsletter promotion, and not the newsletter itself that's at fault.
Consider also how much the new subscribers cost. Perhaps the new subscribers to newsletter A each cost US$10 to acquire through advertising. But newsletter B acquired its new subscribers for 2 cents each. Now which is the most successful newsletter?
You begin to see, I hope, how complex the idea of metrics and success can be. Never consider a number in isolation, and never assume just one explanation or cause for this number.
In general though, the rate of loss of addresses (unsubscribes) is a good indicator of whether your newsletter is meeting the needs of your readers. If not, then either you're attracting the wrong subscribers, or you need to make changes to your publication.
It's often helpful to calculate two unsubscribe numbers. One for new subscribers, i.e. how many are leaving the list soon after subscribing, and one for long-term subscribers, i.e. how many are leaving despite being loyal in the past.
Separating the two can give you a better idea of what's behind a loss of subscribers, for example:
- are you failing to account for the needs of new subscribers?
- are long-term subscribers put off by a recent article or format change?
- is your promotion targeted at the wrong sort of reader?
- are you failing to sustain newsletter value in the long-term?
Finally, always remember that size does not equate to influence. It's quality, not quantity, that counts. If you lose 10% of your readership by changing your newsletter, but your impact and influence on the remaining 90% has improved tremendously, then the loss is a welcome one.
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