• by daniel.c , Melinda Krueger , August 16, 2005

If you're like most e-mail marketers, you think of your unsubscribe rate as an essentially useless statistic. It's a minuscule and consistent percentage of your delivered e-mails. Popular wisdom holds that people find it easier or safer to delete than to unsubscribe. Calculated a slightly different way, your unsubscribe rate can give you new insight into your audience behavior.

The new rate, which I call the Disaffection Index, simply uses a different denominator. Rather than unsubscribe/delivered, the Disaffection Index (DI) is calculated by dividing unsubscribes by the response rate: unsubcribes/unique clicks.

Calculated this way, the DI tells you how many people either a) clicked on your e-mail for the sole purpose of getting off your list or b) were so dissatisfied with the payoff (promise vs. delivery) that they chose to unsubscribe.

Calculated the old way, the unsubscribe rate denominator includes people who never opened the e-mail in the first place, which makes it ineffective in diagnosing the response of those who did.

The DI yields a useful statistic that varies widely from campaign to campaign and audience segment to audience segment. Here is an example of actual results from a series of mailings and a view into the audience segments from a specific mailing. (The mailings are distinct campaigns mailed on different days. The Audience segments are a breakdown of Mailing 7.)

Mailing	Old Unsubscribe Rate	Disaffection Index
Mailing 1	0.2%	2.6%
Mailing 2	0.1%	8.8%
Mailing 3	0.2%	9.0%
Mailing 4	0.1%	0.8%
Mailing 5	0.2%	4.2%
Mailing 6	0.2%	2.3%
Mailing 7	0.2%	6.4%
Breakdown by Audience Segment From Mailing 7
Silver Customers	0.2%	3.0%
Gold Customers	0.1%	1.7%
Platinum Customers	0.1%	1.2%
New Customers	0.5%	9.9%
Lapsed Customers	0.2%	7.4%
Total	0.2%	6.4%

Perhaps the most interesting difference is that campaigns and segments with the lowest "old" unsubscribe rate actually have the highest disaffection index when calculated the new way. This also suggests that it would be wise to subtract unsubscribers from responders prior to calculating click-through rates, in order to separate those who clicked to get more information from those who clicked to get off the e-mail list.

At a recent e-mail conference, mailers wanted to know how to determine when they had reached the saturation point with an audience, i.e., when they had mailed too much. The DI will help to answer this question and show which campaigns truly received the best overall response from your e-mail audience.