Statistics - Percentile Rankings
P.R. are used to compare individual scores to groupe scores. It is called this because a single value is calculated in relation to all there values..


P.R. = (B + 0.5E) . 100
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n
B = the number of scores below the given score
E = the number of scores equal to a given score ( if there are no other scores equal to use 0)
n= the total number of scores



Measures of Variability - Standard Deviation
Range = the diffrence between the largest and the smallest
Standard Deviation = a measure of variability


To calculate the standard deviation of a groupe of numbers it can be determined by using these steps
1. Calculate the mean of the numbers.
2. Determine the diffrence between each number
3. Determine the squares of the differences
4. Determine the sum of these squares
5. Divide the sum of the squares by n -1
6. Calculate the square root of this number

Normal Distributions
Characteristics of the normal curve :
1. Bell Shaped - infanite in both directions
2.Symetric about the mean
3. median
4. is appromiatly all of the data

Correlation Coefficient
Correlation Coefficiant = how to interpret a number that measures a relationship between two sets of values.
Positive Correlation = means that as one variable increases another variable also increases

-1 <> 1
- -
( the range of values for all correlation coefficiants is always between the above)