When a person is describing an incident his story will be comprised of three segments. In the first segment, the subject will tell us what he was doing before the incident occurred. In the second segment, he will describe the incident. In the third segment, the subject will end his story by telling us what he did after the incident was over. We can determine if a story is truthful by examining how much time is devoted towards each of these three segments.
Truthful stories will generally follow a pattern of 25 - 50 - 25. The before incident segment will consist of approximately 25% of the entire statement. Approximately 50% of the story will be about the incident and 25% of the story will be devoted towards the after incident segment.
Deceptive stories generally have a ratio of 35 - 50 - 15. They will have a significant beginning as the subject sets the stage for his bogus tale. The majority of the statement will be devoted towards describing the incident. However, the after incident segment will be very short. A deceptive person usually forgets to include a significant ending to his fabricated story. Once he has told his lie about the incident he thinks that is all he needs to say. In real life, there is always something else going on after the incident is over which usually enters into the statement.
In 2009, I asked 100 people to write a fictional story about being confronted and robbed. 92% of the participants used the 35 - 50 - 15 percentages in writing their deceptive story. They described what they were doing before being robbed. They then described the robbery. After the robbers left the scene and the incident was over, they ended their story very quickly. The far majority of them ended their story by saying they called the police to report the crime. What they did not mention was talking to the police, filing a report, calling a friend, any emotions they were experiencing, etc. Since none of this happened, a deceptive person fails to include this type of information. He focuses more on the incident in trying to make his story sound believable.
One might say the reason 92% of the participants had a very short after incident segment is because they were instructed to write about the incident (the robbery). The problem with this theory is that without instruction all 100 of the participants also wrote about the before incident segment. They were not solely focused on the robbery but wrote about what they were doing before the robbery occurred. However, once they told their lie about the incident they ended their story very quickly.