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Discrete Variables

Variables that can take on a finite set of values (ending)

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Continuous Variables

Variables that can take on an infinite set of values (non-ending)

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Real Limits

An extra tenth, midway between the given value and the next lower/higher value (9.87 = 9.865/9.875)

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Population

An entire set of possible observations that may be made

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Sample

A collection of numbers drawn from a population

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Independent Variable

The variable that is varied or manipulated by the researcher

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Dependent Variable

The response that is measured

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Experimental Study

Describes behavior with identifying the cause

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Non-experimental Study

Describes behavior but does not identify causes

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Quasi-experiment

An observational study with subjects that are already grouped from existing categories

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Nominal Scale

Mutually exclusive categories (category)

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Ordinal Scale

Mutually exclusive categories and logical natural order (ranks)

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Interval/Ratio Scale

Mutually exclusive categories, logical and natural order with equal differences between values

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Histogram

Touching bar graph with interval/ration data

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Bar Chart

Non-touching bar graph with nominal/ordinal data

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Frequency Polygon

Line graph with interval/ratio data

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Unimodal Distribution

One peak in the graph

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Bimodal Distribution

Two peaks in the graph

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Symmetrical Tails

Equidistant lengths from the mean

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Skewed Tails

Differing lengths from the mean

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Kurtosis

How pointed or flat the curve is

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Advantages of Mode

Unaffected by extreme scores, is an actual score in the distribution, can use mode with all data

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Disadvantages of Mode

May not represent data well, can easily be affected by one or two scores

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Advantages of Median

Unaffected by extreme scores, can use with ordinal or interval/ratio data (can represent skewed data)

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Disadvantages of Median

May not represent data well, value you may not exist as a real score, cannot use with nominal data

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Advantages of Mean

Every point contributes to the mean, can be used in equations, unbiased estimate of population

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Disadvantages of Mean

Influenced by extreme scores, can be used with interval/ratio, value may not exist in the data

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Mode = Mean = Median

Any normal distribution

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Use Mode with...

Nominal, Ordinal, Interval/Ratio data

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Use Median with...

Ordinal, Interval/Ration data

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Use Mean with...

Interval/Ratio data

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Variability

Indicates the spread of distribution and the degree to which scores are clustered about the mean

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Measures of Variability

Range, Standard Deviation, Variance

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Degrees of Freedom

The number of values in a data set that can vary

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Inflection Points

A point where a line changes from concave to convex

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Percentiles

Values that divide the distribution into 100 equal parts

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Percentile Rank

A particular person's rank relative to the reference group

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