Thursday, November 5, 2015

Rampage killings and the moon

A friend sent me a note by somebody who contended to have found a statistically significant connection between rampage killings and the full moon. It was based on 60 rampage killers from this wikipedia page:

https://en.wikipedia.org/wiki/List_of_rampage_killers

When I looked over there I found more than 1000 cases were listed. So why test only 60?
I collected all the data on wikipedia into excel, cleaned them out for cases that have no exact date and obtained a sample of 1155 cases.
Using swisseph in excel I could easily test them for proximity to full moon. Moon phase doesn't change quickly, so I set all charts to London noon GMT.

You can download my excel sheet here: https://drive.google.com/file/d/0B38XDYuyyRE_NTZkY05tODF3Znc/view?usp=sharing
(comes as a zip file containing the excel file and a txt file with instructions for use)

I didn't find a higher frequency of rampage killings near full moon, but I found something else with a p value of 0.000013 (binomial)
You can see it in this distribution chart (binned by 20 degree):


In the waning crescent phase of the moon (280 to 360) we have a steadily elevated frequency of rampage killings. In this phase of the moon rampage killings have happened more than 30% more frequently than in the rest of the lunar cycle. This is a high difference.
Normal expectation: 0.2222 (80/360)
Test cases:  1155
Number of successes(x): 318
Cumulative probability P(x >=318) = 0.0000137

That's more unusual than anything I have ever seen come out of a test of astrology, so I have been double checking over and over to find a mistake somewhere, but I can't. If you spot something then please let me know in the comments section.

Because a hypothesis cannot be verified on the same set of data that was used to derive it I will start to keep track of rampage killings as of today Nov 5, 2015. We will then see if this tendency keeps going.
I will be using the same criteria as in the wikipedia article:

"A rampage killer has been defined as follows:
A rampage involves the (attempted) killing of multiple persons least partly in public space by a single physically present perpetrator using (potentially) deadly weapons in a single event without any cooling-off period
This list should contain every case with at least one of the following features:
  • Rampage killings with 6 or more dead (excluding the perpetrator)
  • Rampage killings with at least 4 people killed and a double digit number of victims (dead plus injured)
  • Rampage killings with at least 12 victims (dead plus injured)"
 For each new case we add to the list we will use the date and set time to 12 noon London GMT, just like in the test sample. If the Moon is waning crescent (280-360 angle with the Sun, geocentric) then we have a match, otherwise not. If the hypothesis holds up then we should see more than 22.22% of matching cases (80/360). I will watch the wikipedia pages for new additions, but if you think some rampage killing has been forgotten then you are always welcome to let me know in the comments. If it fits the set criteria then we will add it.


2 comments:

  1. What an elegant experiment! By definition, you have almost a complete data set, and have isolated a simple lunar factor. While no one is looking forward to any more of these killings, they will happen, and now at least some good will come of it as you add them to the data set. I know, that's still kind of sick but it could be the beginnings of some valuable actuarial knowledge. Or yet another meaningless artifact. Time will tell, but what an elegant and exciting design.

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    1. I will have more info later, rampage killings also appear to be seasonal. I am also working on a large study of terrorist attacks, which are distinct from rampage killings.
      Whether the observed hypothesis will keep showing up in future incidents remains to be seen. If it does it may help point the way to potential causes and thus possible solutions/prevention.

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