It is an attempt to understand the dynamics of church growth using mathematics and systems dynamics methods. Most conversion growth comes from contact between an enthusiast and an unbeliever. The numbers converted being proportional to the numbers of both. The model is also called the epidemic model of church growth, or the conversion model. This is referred to as the Simple Church Growth Model or the Limited Enthusiasm Model.
Time scales are short enough that birth and death effects can be ignored.
There is no reversion - people leaving the church. There is no persecution. There is no competition between different religious groups. This depends on the number of unbelievers. The number of enthusiasts does not affect whether such substantial growth occurs, only how long it takes to start.