Local UFO Sightings Recurrency
This is a frequency spectrum of repeat sightings, within 5 minutes of Longitude and Latitude, worldwide, for all years.High counts at 5 years reflect the intervals between the waves in 1947, 1952 and 1957. White dots show counts for 1, 2 .. up to 600 months intervals between locally recurrent sightings. The blue curve is a running average to show trends.
Repeat visits seems to level off, then turn up at 19.5 and 39 year intervals. Attempts to predict future waves based on such data have been dismal failures.
This graph refreshed in July of 2003. Thanks to David Wilson who fixed a botched Copyright notice! It took three hours to generate the image. I'm not about to do that twice.