Brian;

Yes it could make a big difference.

One of the problem with quakes is that they tend to come in clusters and that throws the odds off.

One way of dealing with it, called declustering, is to remove them from the catalog. This is difficult and time consuming.

The Jones method doesn't eliminate the problem but it reduces it dramatically.

Consider a simple example. You have a 300 day period with 50 quakes in it. You might say the odds are 50/300 or 1/6.

However, due to clustering, those 50 quakes all happened in 6 days. So the odds are really 6/300 or 1/50 that a day chosen at random would have a quake in it.

Roger