Psychological Testing and Assessment: An Introduction To Tests and Measurement, 5/e
| Average deviation | A measure of variability derived by summing the absolute value of all the scores in a distribution and dividing by the total number of scores, 87 Banding, 185
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| Bar graph | A graphic illustration of data wherein numbers indicative of frequency are set on the vertical axis, categories are set on the horizontal axis, and the rectangle bars that describe the data are typically noncontiguous, 80
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| Bimodal distribution | A distribution in which the central tendency consists of two scores occurring an equal number of times, both the most frequently occurring scores in the distribution, 85.
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| Distribution | In a psychometric context, a set of test scores arrayed for recording or study, 78
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| Frequency distributions | A tabular listing of scores along with the number of times each score occurred, 78-81
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| Frequency polygon | A graphic illustration of data wherein numbers in-dicating frequency are set on the vertical axis, test scores or categories are set on the horizontal axis, and the data are described by a continuous line connecting the points where the test scores or categories meet frequencies, 80
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| Graph | A diagram or chart composed of lines, points, bars, or other symbols that describe and illustrate data, 80
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| Grouped frequency distribution | A tabular summary of test scores in which the test scores are grouped by intervals; also referred to as class intervals, 78
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| Histogram | A graph with vertical lines drawn at the true limits of each test score (or class interval), forming a series of contiguous rectangles, 80
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| Interquartile range | An ordinal statistic of variability equal to the difference between the third and first quartile points in a distribution that has been divided into quartiles, 86.
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| Interval scale | A system of measurement in which all things measured can be rank-ordered, where the rank-ordering contains equal intervals, every unit on the scale is equal to every other unit on the scale, and there is no absolute zero point; mathematical operations may not be performed on interval-level data because of the absence of a true or absolute zero point, 75, 197-198
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| Kurtosis | An indication of the nature of the steepness (peaked versus flat) of the center of a distribution, 90. See also Platykurtic, Leptokurtic, and Mesokurtic
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| Leptokurtic | A description of the kurtosis of a distribution where the distribution is relatively peaked in its center, 90.
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| Mean | Also called the arithmetic mean, a measure of central tendency derived by calculating an average of all scores in a distribution, 81, 83
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| Measurement | Assigning numbers or symbols to characteristics of people or objects according to rules, 15-16, 73
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| Measure of central tendency | A statistic indicating the average or middlemost score between the extreme scores in a distribution. The mean is a measure of central tendency and a statistic at the ratio level of measurement; the median is a measure of central tendency that takes into account the order of scores and is ordinal in nature; the mode is a measure of central tendency that is nominal in nature, 81-85.
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| Median | A measure of central tendency derived by identifying the middlemost score in a distribution, 83-84
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| Mesokurtic | A description of the kurtosis of a distribution where the distribution is not extremely peaked or flat in its center, 90. See also Kurtosis
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| Mode | A measure of central tendency derived by identifying the most frequently occurring score in a distribution, 84-85.
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| Nominal scale | A system of measurement in which all things measured are classified or categorized based on one or more distinguishing characteristics and placed into mutually exclusive and exhaustive categories, 74
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| Normal curve | A bell-shaped, smooth, mathematically defined curve highest at the center and gradually tapered on both sides, approaching but never actually touching the horizontal axis, 90-94
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| Normalized standard score scale | Conceptually, the end product of "stretching" a skewed distribution into the shape of a normal curve, usually through nonlinear transformation, 98
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| Ordinal scale | A system of measurement in which all things measured can be rank-ordered, where the rank-ordering implies nothing about exactly how much greater one ranking is than another and there is no absolute zero point on the scale; most scales in psychology and education are ordinal, 74-75, 194-197
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| Platykurtic | A description of the kurtosis of a distribution where the distribution is relatively flat in its center, 90.
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| Quartile | One of three dividing points between the four quarters of a distribution, each typically labeled Q1, Q2, or Q3, 86
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| Range | A descriptive statistic of variability derived by calculating the difference between the highest and lowest scores in a distribution, 86
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| Ratio scale | A system of measurement in which all things measured can be rank-ordered, the rank ordering does imply something about exactly how much greater one ranking is than another, equal intervals exist between each number on the scale, and all mathematical operations can be performed meaningfully because a true or absolute zero point exists; few scales in psychology or education are ratio scales, 76
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| Scale | (1) A system of ordered numerical or verbal descriptors, usually occurring at fixed intervals, used as a reference standard in measurement; (2) a set of numbers or other symbols whose properties model empirical properties of the objects or traits to which numbers or other symbols are assigned, 16, 73-76, 194
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| Semi-interquartile range | A measure of variability equal to the inter-quartile range divided by two, 86.
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| Skewness | An indication of the nature and extent to which symmetry is absent in a distribution; a distribution is said to be skewed positively when relatively few scores fall at the positive end and skewed negatively when relatively few scores fall at the negative end, 89-90
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| Standard deviation | A measure of variability equal to the square root of the averaged squared de-viations about the mean; a measure of variability equal to the square root of the variance, 87-89.
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| Standard score | A raw score that has been converted from one scale into another, the latter scale (1) having some arbitrarily set mean and standard deviation and (2) being more widely used and readily interpretable; examples of standard scores are z scores and T scores, 94-98
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| Stanine | A standard score derived from a scale with a mean of 5 and a standard deviation of approximately 2, 96-97
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| T score | Named for Thorndike, a standard score calculated using a scale with a mean set at 50 and a standard deviation set at 10; the measure of choice for the developers of the MMPI (As technical problems emerged in the scoring of MMPI protocols with T scores, some researchers suggested that these scores be replaced with normalized T scores; ultimately the developers of the MMPI-2 agreed to use what they called a uniform T score or UT), 95-96, 350
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| Variability | An indication of how scores in a distribution are scattered or dispersed, 85-89
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| Variance | A measure of variability equal to the arithmetic mean of the squares of the differences between the scores in a distibution and their mean, 87, 88, 129
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| z score | A standard score derived by calculating the difference between a particular raw score and the mean, divided by the standard deviation; a z score expresses a score in terms of the number of standard deviation units the raw score is below or above the mean of the distribution, 94-95
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2002 McGraw-Hill Higher Education