midterms

• Continuous scales


  Theoretically possible to divide any of the values of the scale. Typically having a wide range of possible values (e.g. height or a depression scale)
• Discrete scales


  Categorical values (e.g. male or female)
• Error


  The collective influence of all of the factors on a test score beyond those specifically measured by the test
• Nominal Scales


  Involve classification or categorization based on one or more distinguishing characteristics; all things measured must be placed into mutually exclusive and exhaustive categories (e.g. apples and oranges, DSM-IV diagnoses, etc.)
• Ordinal Scales


  Involve classifications, like nominal scales but also allow rank ordering (e.g. Olympic medalists)
• Interval Scales


  Contain equal intervals between numbers. Each unit on the scale is exactly equal to any other unit on the scale (e.g. IQ scores and most other psychological measures)
• Ratio Scales


  Interval scales with a true zero point (e.g. height or reaction time)
• Psychological Measurement - Most psychological measures are truly ordinal but are treated as interval measures for statistical purposes
• Distributions


  A set of test scores arrayed for recording or study
• Raw Score


  A straightforward, unmodified accounting of performance that is usually numerical
• Frequency Distribution


  All scores are listed alongside the number of times each score occurred
• Bar graph


  Numbers indicative of frequency appear on the Y-axis, and reference to some categorization (e.g., yes/no/ maybe, male/female) appears on the X-axis
• Frequency polygon


  Test scores or class intervals (as indicated on the X-axis) meet frequencies (as indicated on the Y-axis)
• Central tendency


  A statistic that indicates the average or midmost score between the extreme scores in a distribution
• Mean


  Sum of the observations (or test scores), in this case divided by the number of observations
• Median


  The middle score in a distribution. Particularly useful when there are outliers, or extreme scores in a distribution
• Mode


  The most frequently occurring score in a distribution. When two scores occur with the highest frequency a distribution is said to be bimodal
• Variability


  An indication of the degree to which scores are scattered or dispersed in a distribution
• Measures of variability


  Statistics that describe the amount of variation in a distribution
• Range


  Difference between the highest and the lowest scores
• Interquartile range


  Difference between the third and first quartiles of a distribution
• Semi-interquartile range


  The interquartile range divided by 2
• Average deviation


  The average deviation of scores in a distribution from the mean
• Variance


  The arithmetic mean of the squares of the differences between the scores in a distribution and their mean
• Standard deviation


  The square root of the average squared deviations about the mean. It is the square root of the variance. Typical distance of scores from the mean
• Skewness


  The nature and extent to which symmetry is absent in a distribution
• Positive skew


  Relatively few of the scores fall at the high end of the distribution
• Negative skew


  Relatively few of the scores fall at the low end of the distribution
• Continuous scales


  Theoretically possible to divide any of the values of the scale. Typically having a wide range of possible values (e.g. height or a depression scale)
• Kurtosis


  The steepness of a distribution in its center
• Discrete scales


  Categorical values (e.g. male or female)
• Error


  The collective influence of all of the factors on a test score beyond those specifically measured by the test
• Platykurtic


  Relatively flat
• Nominal Scales


  Involve classification or categorization based on one or more distinguishing characteristics; all things measured must be placed into mutually exclusive and exhaustive categories (e.g. apples and oranges, DSM-IV diagnoses, etc.)
• Ordinal Scales


  Involve classifications, like nominal scales but also allow rank ordering (e.g. Olympic medalists)
• Interval Scales


  Contain equal intervals between numbers. Each unit on the scale is exactly equal to any other unit on the scale (e.g. IQ scores and most other psychological measures)
• Leptokurtic


  Relatively peaked
• Ratio Scales


  Interval scales with a true zero point (e.g. height or reaction time)
• Most psychological measures are truly ordinal but are treated as interval measures for statistical purposes
• Distributions


  A set of test scores arrayed for recording or study