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Quaking Up The Stats

21 December 2011, 06:59

Breinlekkasie had to respond to some of the comments on the article “No rise in big quakes – study”.  One of the readers listed a number of websites which supposedly contradict the article in question but my hunch is that the reader lacks an understanding of probability theory (the math that explains why one cannot beat the house at cards).

Despite the fact that there were more earthquakes since 2007 the probability of a quake taking place propagates to the mean (statistical average).  This increase is countered by the fact that far less quakes were recorded during the period 1965 until 2007.  Over enough time the number of quakes will average out to a particular mean which is more or less random even though there are spikes and down spikes in the number of quakes from time to time.

This increase of earthquakes can be explained by comparing it to the probability of a tossed coin falling heads up or tails up.  There is only a 50% probability that a coin will fall on either side.  If one tosses a coin say five times and three out of the five tosses result in heads up does that mean there is an increase from 50% to 60% in the probability that the coin will fall heads up in future?  No.

The probability remains only 50% since one can expect that the coin will fall tails up more often in future.  However the occurrence of a heads up or tails up per toss is not predictable even though one can expect that the coin will fall less often on tails in the near future to converge back to the statistical average of 50%.

However if one should rig the coin by making it heavier on the head side the probability will change and the coin will fall heads up more often but this is because of a definite external change to the homogeneity of the material the coin was made of.  Even so if the coin falls 70% heads up after the change it will converge back to its mean of 70% even if one manage to measure 7 tails up landings out of ten tosses.

A sudden increase in earthquakes over a period of two or three years is no indication that the probability of earthquake occurrences is increasing.  One can only expect that earthquakes will take place less often in the future in a non predicable manner to converge back to the statistical average.  Without a definite change (explanation) in the earth’s crust one can safely conclude there shall be no increase in the probability of earthquakes.

Often people make this mistake thinking that a sudden increase or decrease in the number of particular events are acts of God yet they are merely natural spikes and down spikes that evens out to the statistical average.

I can’t explain this any better without writing a book on the subject.

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