Basics of statistics

MEAN
Average (Mean) = Sum of measurements / Number of measurements

MEDIAN
Middle value  after arranging items in an order

MODE
Most frequently occurring value from data set

RANGE
Highest value - Lowest value

STANDARD DEVIATION
Sqrt of (Average of (Squared deviations of the items from their mean value))

VARIENCE
Average of Squared differences from their mean value
Example : {600, 470, 170, 430, 300}
                 M (Mean) = 600 + 470 + 170 + 430 + 300 = 1970/5 = 394
                 sqr(600-394) + sqr(470-394) + sqr(170-394) + sqr(430-394) + sqr(300-394) =
                 sqr(206) + sqr(76) + sqr(−224) + sqr(36) + sqr(−94)
                 (42,436 + 5,776 + 50,176 + 1,296 + 8,836) = 108,520 
                 Varience = 108,520 / 5 = 21,704

NORMAL DISTRIBUTION
Arrangement of data set where most values cluster in the middle of the range and rest towards either extreme.
Its graphical representation is called BELL CURVE.
Mean, mode and median are all the same.

HISTOGRAM
Graphical representation of the distribution of numerical data.