RCMP Environmental Scan

A very nice document prepared by the RCMP, and publicly available.

It covers demographics, society, economy, politics & government, science & technology, environment and public safety & security at both the global and Canadian levels.

Link: http://www.rcmp.gc.ca/enviro/2007/index_e.htm

Kurtosis

Kurtosis is the degree to which the frequency distribution is concentrated around a peak, that is, it describes the sharpness of the central peak of the curve, usually as compared with the normal distribution.

Higher kurtosis means more of the variance is due to infrequent extreme deviations (more variance, less concentrated around the mean), as opposed to frequent modestly-sized deviations (less variance, more concentration around the mean)

The normal distribution is mesokurtic; the curve with a higher degree of kurtosis (peakedness) is leptokurtic; and the curve with the flat top (compared to the normal curve) is platykurtic.

Links:

http://www.riskglossary.com/articles/kurtosis.htm

http://mvpprograms.com/help/mvpstats/distributions/SkewnessKurtosis

http://www.statistics4u.info/fundstat_eng/cc_kurtosis.html

http://www.almprofessional.com/Articles/skew.pdf

http://www.ats.ucla.edu/stat/spss/faq/kurtosis.htm

Mean Absolute Deviation

The mean deviation is the mean of the absolute deviations of a set of data about the data's mean.

Mean deviation is an important descriptive statistic that is not frequently encountered in mathematical statistics. The mean deviation has a natural intuitive definition as the "mean deviation from the mean".

The average absolute deviation from the mean is less than or equal to the standard deviation.

When applied to time series, the mean absolute deviation becomes a measure of volatility.

Standard Deviation

Standard deviation is a measure of dispersion. It is defined as the square root of the variance. It measures how widely spread the values in a data set are. If many data points are close to the mean, then the standard deviation is small; if many data points are far from the mean, then the standard deviation is large. In a loose sense, the standard deviation tells us how far from the mean the data points tend to be. The standard deviation has the same units as the data points themselves.

When applied to time series, standard deviation becomes a measure of volatility.

See also: http://www.childrensmercy.org/stats/definitions/stdev.htm
http://www.quickmba.com/stats/standard-deviation/