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Standard Deviation
- average deviation from the mean in the original
- unit of measurement.
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Normal distributions
the mean, mode, and median are the same. Bell-shaped & symmetrical
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Positively-skewed
distribution
majority of scores on the lower end of range (the mean is more positive than mode and median).
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Negatively-skewed
majority of scoreson the higher end (mean is more negative than mode and median.
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Reliability
consistent,true. Is a psychometric indicator ofquality of an instrument. Consistencywhen test is repeated.
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Reliability coefficients
- can be calculated to provide an indication of
- the amount of measurement error.
- Example: on a 0-1 scale, .8=80% reliability. Based on the amount of consistency between
- two sets of scores.
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Correlation
- the statistical technique used to calculate this
- consistency
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Positive correlation
scores are consistent in the same direction
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Negative correlation
scores are consistent in different directions, so as scores on one test increase, scores on another decrease
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Standard Error of Measurement (SEM)
helpful in interpreting an individual’s score. Provides an estimation of the range of scores that would be obtained if someone took an instrument over and over again. Takes reliability into account.
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Validity
- concerns what an instrument measures and how well it does it. Instruments are not valid, uses of instruments are.
- *Reliability is a prerequisite to validity. If there is too much error, the instrument can’t measure anything consistently.
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Convergent evidence
positive relationship of instrument with other variables with which it should theoretically be related. *High=if it agrees
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Discriminant evidence
no relationship or negative relationship of instrument with variables from which it should differ in these ways. *Low=it disagrees. (Happiness/stress/anxiety)
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Norm-referenced
in comparison to others
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Norming group
group who took the instrument to which others’ scores are then compared
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Mode
most frequent score in a distribution
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Median
the score where half the people had a score below it and half had a score above, evenly dividing the scores in half
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Mean
average of the scores
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Frequency Distribution
Can interpret scores more accurately if scores are tallied this way. (Ex: clas has 30 students, these are their scores....)
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Normal curve
- largest mumber of cases cluster in center (68)
- Bell-shpaed
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Scales of Measurement
Nominal, Ordinal, Interval, Ratio
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Nominal
- Numbers are used to classify and identify persons
- Numbers are substituted for names or verbal labels
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Ordinal
Assigns numbers in rank order
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Interval
Helps when interested in differences or intervals between things
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Ratio
- Only scale where you can say "twice as...x"
- Ratios between the umbers assigned to the person or object
- Corresponds to the ratios between the attributes measured in these things
- Addresses issues of relative size, weight, speed, etc. of 2 objects
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