| Bar graph | A graphic way of illustrating differences among groups.
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| Categorical data | Data (variables) that differ only in kind, not in amount or degree.
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| Correlation coefficient | A decimal number between .00 and +1.00 and –1.00 that indicates the degree to which two quantitative variables are related.
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| Crossbreak table | A table that shows all combinations of two or more categorical variables and portrays the relationship (if any) between the variables.
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| ETA | An index that indicates the degree of a curvilinear relationship.
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| Five-number summary | Consists of the lowest score, the first quartile, the median, the third quartile, and the highest score. This summary provides a quick overview about the central tendency, variability, and shape of the distribution with just five numbers.
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| Frequency distribution | A tabular method of showing all the scores obtained by a group of individuals.
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| Frequency polygon | A graphic method of showing all of the scores obtained by a group of individuals.
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| Mean | The sum of the scores in a distribution divided by the number of scores in the distribution; the most commonly used measure of central tendency.
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| Measures of central tendency | Indices representing the average or typical score attained by a group of subjects; the most commonly used in educational research are the mean and the median.
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| Median | That point in a distribution having 50 percent of the scores above it and 50 percent of the scores below it.
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| Mode | The score that occurs most frequently in a distribution of scores.
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| Negatively skewed | A distribution in which there are more extreme scores at the lower end than at the upper, or higher, end.
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| Normal distribution | A theoretical "bell-shaped" distribution having a wide application to both descriptive and inferential statistics. It is known or thought to portray many human characteristics in "typical" populations.
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| Outlier | Scores or other observations that deviate or fall considerably outside most of the other scores or observation in a distribution or pattern.
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| Parameter | A numerical index describing a characteristic of a population.
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| Pie chart | A graphic method of displaying the breakdown of data into categories.
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| Positively skewed | A distribution in which there are more extreme scores at the upper, or higher, end than at the lower end.
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| Probability | The relative frequency with which a particular event occurs among all events of interest.
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| Qualitative data | Data that are not numerical.
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| Quantitative data | Data that differ in amount or degree, along a continuum from less to more.
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| Range | The difference between the highest and lowest scores in a distribution; measure of variability.
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| Scatterplot | The plot of points determined by the cross-tabulation of scores on coordinate axes; used to represent and illustrate the relationship between two quantitative variables.
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| Standard deviation | The most stable measure of variability; it takes into account each and every score in a distribution.
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| Standard score | A derived score that expresses how far a given raw score is from the mean, in terms of standard deviation units.
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| Statistic | A numerical index describing a characteristic of a sample.
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| T score | A score derived from a z score by multiplying the z score by 10 and adding 50.
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| Variance | The square of the standard deviation; a measure of variability.
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| z score | The most basic standard score that expresses how far a score is from a mean in terms of standard deviation units.
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