Introductory Statistics

Key Terms

Degrees of Freedom (df)
the number of objects in a sample that are free to vary.
Pooled Proportion
estimate of the common value of p1 and p2.
Standard Deviation
A number that is equal to the square root of the variance and measures how far data values are from their mean; notation: s for sample standard deviation and σ for population standard deviation.
Variable (Random Variable)
a characteristic of interest in a population being studied. Common notation for variables are upper-case Latin letters X, Y, Z,... Common notation for a specific value from the domain (set of all possible values of a variable) are lower-case Latin letters x, y, z,.... For example, if X is the number of children in a family, then x represents a specific integer 0, 1, 2, 3, .... Variables in statistics differ from variables in intermediate algebra in the two following ways.
• The domain of the random variable (RV) is not necessarily a numerical set; the domain may be expressed in words; for example, if X = hair color, then the domain is {black, blond, gray, green, orange}.
• We can tell what specific value x of the random variable X takes only after performing the experiment.
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