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Basic Assessment Principles Chapter 2
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Nominal Ordinal Interval Ratio Measurement Scales
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Individual’s score is compared to performance of others who have taken the same instrument (norming group) Example: personality inventory Evaluating the norming group size sampling representation Norm-Referenced Instruments
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Individual’s performance is compared to specific criterion or standard Example: third-grade spelling test How are standards determined? common practice professional organizations or experts empirically-determined Criterion-Referenced Instruments
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Robert 72 Miles 96 Jason 68 Whitney 79 Alice 82 Paul 59 Pedro 86 Jane 85 Beth 94 John 82 Kelly 92 Michael 81 Amy 77 Kevin 85 Justin 72 Rebecca 88 Porter 62 Ling 98 Sherry 67 Maria 86 Norm-Referenced: Sample Scores
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Frequency Distribution
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Frequency Polygon
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Histogram
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Measures of Central Tendency Mode – most frequent score Median – evenly divides scores into two halves (50% of scores fall above, 50% fall below) Mean – arithmetic average of the scores Formula:
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Measures of Central Tendency Example: Sample scores – 98, 98, 97, 50, 49 Mode = 98 Median = 97 Mean = 78.4
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Measures of Variability Range – highest score minus lowest score Variance – sum of squared deviations from the mean Standard Deviation – square root of variance Formula:
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Normal Distribution
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Skewed Distribution
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Raw scores Percentile scores/Percentile ranks Standard scores z scores T scores Stanines Age/grade-equivalent scores Types of Scores
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Percentiles
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98 th percentile 98% of the group had a score at or below this individual’s score 32 nd percentile 32% of the group had a score at or below this individual’s score If there were 100 people taking the assessment, 32 of them would have a score at or below this individual’s score Interpreting Percentiles
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Units are not equal Useful for providing information about relative position in normative sample Not useful for indicating amount of difference between scores Interpreting Percentiles
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Types of Standard Scores
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z Scores z score = X-M s Mean = 0 Standard deviation = 1
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Mean = 50 Standard deviation = 10 T Scores
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Stanines
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Standard Scores: Summary
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Possible problematic scores Age-equivalent scores Grade-equivalent scores Problematic because: These scores do not reflect precise performance on an instrument Learning does not always occur in equal developmental levels Instruments vary in scoring Additional Converted Scores
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Adequacy of norming group depends on: Clients being assessed Purpose of the assessment How information will be used Examine methods used for selecting group Examine characteristics of norming group Evaluating the Norming Group
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Methods for selecting norming group: Simple random sample Stratified sample Cluster sample Sampling Methods
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Size Gender Race/ethnicity Educational background Socioeconomic status Is the norming group appropriate for use with this client? Norming Group Characteristics
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