# Appendix A. Descriptive Statistics Statistics used to organize and summarize data in a meaningful way.

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Appendix A

Descriptive Statistics

Statistics used to organize and summarize data in a meaningful way

Frequency Distributions

A summary of how often various scores occur in a sample of scores. Score values are arranged in order of magnitude, and the number of times each score occurs is recorded

Histogram

A way of graphically representing a frequency distribution; a type of bar chart that uses vertical bars that touch

Frequency polygon

a way a graphically representing a frequency distribution; frequency is marked above each score category on the graph’s horizontal axis, and the marks are connected by straight lines

Skewed Distributions

An asymmetrical distribution; more scores occur on one side than the other; In a positively skewed distribution, more scores are low

Symmetrical Distribution

A distribution in which the scores fall equally on both sides of the graph, the normal curve is an example

Measure of Central Tendency

A single number that presents some information about the “center” of a frequency distribution

Mode

The most frequent occurring score in a distribution

Median

The score that divides a frequency in half, so that the same number of scores lie one both sides

Mean

The sum of a set of scores in a distribution divided by the number of scores; the mean is usually the most representative measure of central tendency

Measure of Variability

A single number that presents information about the spread of scores in a distribution

Range

A measure of variability; the highest score distribution minus the lowest score

Standard Deviation

A measure of variability; expressed as the square root of the sum of the squared deviations around the mean divided by the number of scores in the distribution

z Score

A number, expressed in standard deviation units, that shows a score’s deviation from the mean

Standard Normal Curve

A symmetrical distribution forming a bell- shaped curve in which the mean, median, and mode are all equal and fall in the exact middle

Correlation

The relationship between two variables

Correlation Coefficient

A measure of the magnitudes and directions of the relationships between two variables. The closer the correlation is to +1 or –1, the stronger the relationship is. A positive correlation coefficient indicates that as one variable increase, the other tends to increase, the negative correlation coefficient indicates as one variable increases, the other tends to decrease

Scatter Diagram

A graph that represents the relationship between two variables

Inferential Statistics

Statistical techniques that allow researchers to determine whether the outcomes in a study are likely to be more than just chance events and whether they can legitimately generalized to a larger population

Population

A complete set of something-people, nonhuman animals, objects, or events

Sample

A subset of a population

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