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Scales of Measurement n Nominal classificationlabels mutually exclusive exhaustive different in kind, not degree

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Scales of Measurement n Ordinal rank ordering numbers reflect “greater than” only intraindividual hierarchies NOT interindividual comparisons

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Scales of Measurement n Interval equal units on scale scale is arbitrary no 0 point meaningful differences between scores

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Scales of Measurement n Ratio true 0 can be determined

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Contributions of each scale n Nominal u creates the group n Ordinal u creates rank (place) in group n Interval u relative place in group n Ratio u comparative relationship

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Graphing data n X Axis horizontalabscissa independent variable

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n Y Axis verticalordinate dependent variable

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Types of Graphs n Bar graph qualitative or quantitative data nominal or ordinal scales categories on x axis, frequencies on y discrete variables not continuous not joined

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Bar Graph

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Types of Graphs n Histogram quantitative data continuous (interval or ratio) scales

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Histogram

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Types of Graphs n Frequency polygon quantitative data continuous scales based on histogram data use midpoint of range for interval lines joined

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Frequency Polygon

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Interpreting Scores

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Measures of Central Tendency n Mean n Median n Mode

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Measures of Variability n Range n Standard Deviation

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Effect of standard deviation

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Assumptions of Normal Distribution (Gaussian) n The underlying variable is continuous n The range of values is unbounded n The distribution is symmetrical n The distribution is unimodal n May be defined entirely by the mean and standard deviation

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Normal Distribution

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Terms of distributions n Kurtosis n Modal n Skewedness

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Skewed distributions

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Linear transformations n Expresses raw score in different units n takes into account more information n allows comparisons between tests

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Linear transformations n Standard Deviations + or - 1 to 3 n z score 0 = mean, - 1 sd = -1 z, 1 sd = 1 z n T scores u removes negatives u removes fractions u 0 z = 50 T

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Example T = (z x 10) + 50 If z = 1.3 T = (1.3 x 10) +50 = 63

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Example T = (z x 10) + 50 If z = -1.9 T = (-1.9 x 10) +50 = 31

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Linear Transformations

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Examples of linear transformations

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Chapter 3 - assignment n Which scale is used for your measure? u Is it appropriate? Are there alternates? n How will you graph the data from your measure?

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