What Does Retention Indicate?
Retention is simply additions minus losses. In our fellowship, additions could either be baptisms or restorations. Losses could be for any number of spiritual reasons, but would exclude people simply moving to a different city.
Same Growth, Different Dynamic
The problem with focusing on growth alone is that two churches can grow equally fast (say, both by 10% in one year) but one by "churning" through people and one by more healthy means.
Take two churches that grow from 500 to 1,000 members in ten years. Church A is a "churning" church and loses seven members for every ten it adds. At this rate of retention, to grow to 1,000 members, Church A must add 1,667 new members, to compensate for the loss of over 1,167 members it will suffer over the same time. (Here's the math: 1,667 * 30% = 500.)
Church B, on the other hand, loses only three members for every ten it adds, so it will achieve the same net growth with only 714 additions. (Again, 714 * 70% = 500.)
Keep in mind, on a superficial level both churches have grown by exactly the same amount, at exactly the same rate of growth. Clearly, though, it more likely that Church B is using more spiritual, sustainable ways to grow.
The ICOC and Retention
Overall from 1999-2002, the average congregation in the ICOC lost 7.8 members for every 10 additions. Only a few of the largest 100 churches were able to retain more than five members for every ten additions in this period. There is a cumulative effect to growing churches with low retention rates: over time, the number of ex-members in any given church's area will grow to exceed the number of members, no matter how fast it grows.
In the example above, after ten years Church A has 1,000 members but also 1,167 new ex-members. After ten more years of the same growth, ex-members will outnumber members by almost two to one. For Church B, however, its ex-members will never outnumber members as long as it maintains the same retention.
Social Networks and Their Impact on High Growth/Low Retention Churches
Rodney Stark, a sociologist who applied the tools of his field to the study of church history, both modern and ancient, argues forcefully that "attachments lie at the heart of conversion and therefore...conversion tends to proceed along social networks formed by interpersonal attachments." Extending this idea, social attachments would have an equally strong impact on the decision to leave a church.
In its early years the movement that later became the ICOC cited high retention rates along with high growth rates. By 1996, its leaders were openly acknowledging their churches were growing but with very low retention rates, losing as many as seven members for every ten new members added.
By 2002, in many cities this high-growth, low-retention combination meant that most members may well have known and had close attachments with more ex-members than members. The impact of reaching this "tipping point" may well have been the proximate cause of the unprecedented losses many churches experienced in 2003.