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S3.2 - Measures of Dispersion
Measures of Dispersion
23
Mathematics
Graduate
11/04/2013

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Term
Dispersion
Definition
The degree to which the data are spread out
Term
Range
Definition
The difference between the largest data value and the smallest data value (R)
Term
Range =
Definition
Largest data value - smallest data value
Term
Deviation about the mean
Definition
For the i-th observation is (xi - mew)
Term
Sample deviation about the mean
Definition
For the i-th observation is (xi - xbar)
Term
The sum of all deviations about the mean must equal
Definition
0
Term
Population variance (sigma^2)
Definition
The sum of the squared deviations about the population mean divided by the number of observations in the population (N)
Term
1. Population variance, sigma^2 =
Definition
Summation(xi-mew)^2/N
Term
2. Population variance, sigma^2 =
Definition
Summation(xi^2 - (summation(xi)^2)/N)/N
Term
Sample variance, s^2
Definition
Determining the sum of the squared deviations about the sample mean and dividing it by n-1
Term
1. Sample variance, s^2 =
Definition
Summation(xi-xbar)^2/n-1
Term
2. Sample variance, s^2 =
Definition
Summation(xi^2 - (summation(xi)^2)/n)/n-1
Term
Biased
Definition
Whenever a statistic consistently over/underestimates a parameter
Term
Degree of freedom
Definition
The number of independent ways by which a dynamic system can move without violating any constraint imposed on it
Term
Population standard deviation, sigma =
Definition
(sigma^2)^(1/2)
Term
Sample standard deviation, s =
Definition
(s^2)^(1/2)
Term
Standard deviation typically represents
Definition
A typical deviation from the mean
Term
The (larger/smaller) the standard deviation, the more dispersion the distribution has
Definition
Larger
Term
1. Empirical Rule - Normal Distribution
Definition
1 standard deviation from the mean should include 68% of the data; 68% lies between (mew-1sigma) and (mew+1sigma)
Term
2. Empirical Rule - Normal Distribution
Definition
2 standard deviations from the mean should include 95% of the data; 95% lies between (mew-2sigma) and (mew+2sigma)
Term
3. Empirical Rule - Normal Distribution
Definition
3 standard deviations from the mean should include 99.7% of the data; 99.7% lies between (mew-3sigma) and (mew+3sigma)
Term
Chebyshev's inequality determines
Definition
The minimum percentage of observations within a distribution for a given standard deviation
Term
Chebyshev's inequality =
Definition
(1-1/k^2)100%
where k = standard deviation
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