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Discrete Variables

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

Continuous Variables

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

Real Limits

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

Population

An entire set of possible observations that may be made

Sample

A collection of numbers drawn from a population

Independent Variable

The variable that is varied or manipulated by the researcher

Dependent Variable

The response that is measured

Experimental Study

Describes behavior with identifying the cause

Non-experimental Study

Describes behavior but does not identify causes

Quasi-experiment

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

Nominal Scale

Mutually exclusive categories (category)

Ordinal Scale

Mutually exclusive categories and logical natural order (ranks)

Interval/Ratio Scale

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

Histogram

Touching bar graph with interval/ration data

Bar Chart

Non-touching bar graph with nominal/ordinal data

Frequency Polygon

Line graph with interval/ratio data

Unimodal Distribution

One peak in the graph

Bimodal Distribution

Two peaks in the graph

Symmetrical Tails

Equidistant lengths from the mean

Skewed Tails

Differing lengths from the mean

Kurtosis

How pointed or flat the curve is

Advantages of Mode

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

Disadvantages of Mode

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

Advantages of Median

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

Disadvantages of Median

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

Advantages of Mean

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

Disadvantages of Mean

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

Mode = Mean = Median

Any normal distribution

Use Mode with...

Nominal, Ordinal, Interval/Ratio data

Use Median with...

Ordinal, Interval/Ration data

Use Mean with...

Interval/Ratio data

Variability

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

Measures of Variability

Range, Standard Deviation, Variance

Degrees of Freedom

The number of values in a data set that can vary

Inflection Points

A point where a line changes from concave to convex

Percentiles

Values that divide the distribution into 100 equal parts

Percentile Rank

A particular person's rank relative to the reference group