To whom it may concern: The most cynical approach to mass-shootings.
An incomplete list of all mass-shootings of 2013 (so far)
http://www.reddit.com/r/GunsAreCool/wiki/2013massshootings
The naval yard in DC was No.247
Huffpost compiled a list of the 17 mass-shootings where at least 4 people were killed.
http://www.huffingtonpost.com/2013/09/17/mass-shootings-2013_n_3941889.html
When will be the next one?
Here's how you can find out! All you need is pen, paper and a scientific calculator:
1. Calculate the average time-span between mass-shootings of a chosen category.
2. Insert that as the rate-parameter into a probability-density-function P(t) that approaches 100% exponentially from below as time goes to infinity. Don't forget to normalize, you little rascals!
3. Calculate the exact dates this year, when the risk of a mass-shooting (calculated by integrating the function from t=0 to an arbitrary date) will reach a given threshold, e.g. 50%, 90%, 99%...
You could mark the days in your calendar!
What an interesting activity for your spare time!
Better use a pencil in your calendar: Once the mass-shooting actually happens, you have to start over with counting and marking days! The formula only predicts the next single mass-shooting, not several mass-shootings of the future.
The formula will stay accurate for a long time though, because nothing about gun-laws and gun-violence will ever change!