| bar graph | Using bars to depict frequencies of responses, percentages, or means in two or more groups.
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| central tendency | A single number or valuethat describes the typical or central score among a set of scores.
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| correlation coefficient | An index of how strongly two variables are related to each other.
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| descriptive statistics | Statistical measures that describe the results of a study; descriptive statistics include measures of central tendency (e.g., mean), variability (e.g., standard deviation), and correlation (e.g., Pearson r).
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| effect size | The extent to which two variables are associated. In experimental research, the magnitude of the impact of the independent variable on the dependent variable.
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| frequency distribution | An arrangement of a set of scores from lowest to highest that indicates the number of times each score was obtained.
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| frequency polygon | A graphic display of a frequency distribution in which the frequency of each score is plotted on the vertical axis, with the plotted points connected by straight lines.
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| interval scale | A scale of measurement in which the intervals between numbers on the scale are all equal in size.
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| mean | A measure of central tendency, obtained by summing scores and then dividing the sum by the number of scores.
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| median | A measure of central tendency; the middle score in a distribution of scores that divides the distribution in half.
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| mode | A measure of central tendency; the most frequent score in a distribution of scores.
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| multiple correlation | A correlation between one variable and a combined set of predictor variables.
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| nominal scale | A scale of measurement with two or more categories that have no numerical (less than, greater than) properties.
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| ordinal scale | A scale of measurement in which the measurement categories form a rank order along a continuum.
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| partial correlation | The correlation between two variables with the influence of a third variable statistically controlled for.
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| path analysis | A method used to develop models of possible relationships among a set of variables that were studied with the nonexperimental method.
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| pearson product-moment correlation coefficient | A type of correlation coefficient used with interval and ratio scale data. In addition to providing information on the strength of relationship between two variables, the Pearson product-moment correlation coefficient indicates the direction (positive or negative) of the relationship.
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| pie chart | Graphic display of data in which frequencies or percentages are represented as "slices" of a pie.
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| ratio scale | A scale of measurement in which there is an absolute zero point, indicating an absence of the variable being measured. An implication is that ratios of numbers on the scale can be formed (generally, these are physical measures such as weight or timed measures such as duration or reaction time).
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| regression equation | A mathematical equation that allows prediction of one behavior when the score on another variable is known.
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| standard deviation | The average deviation of scores from the mean (the square root of the variance).
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| statistical significance | Rejection of the null hypothesis when an outcome has a low probability of occurrence (usually .05 or less) if, in fact, the null hypothesis is correct.
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| structural model | A model of an expected pattern of relationships among a set of variables. The proposed pattern is based on a theory of how the variables are causally related to one another.
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| variability | The amount of dispersion of scores about some central value.
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| variance | A measure of the variability of scores about a mean; the mean of the sum of squared deviations of scores from the group mean.
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