PSYCH 100A Lecture Notes - Lecture 5: Beck Depression Inventory, Null Hypothesis, Standard Score

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Published on 28 Mar 2018
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Lecture 5
Standardized Score Scales
Psychological variables (depression, narcissism) does not have inherent score scales
o We make up the metrics
Researchers use universal metrics
IQ Scale
Uses standard score scale with a mean of 100 and standard deviation of 15
The scale is completely made up
MMPI
Minnesota Multiphasic Personality Inventory
o Widely used test of adult personality and psychopathology
T-Scores
Many psychological tests use a t-score scale with a mean of 50 and standard deviation of
10
Z-scores
A common standard score in psychology and statistics that uses a generic scale with a
mean of 0 and standard deviation of 1
Anything negative is below average
Importance of z-scores
o Any continuous variable can be converted to a z-score
o Can be used to describe scores, characterize difference between distributions
Beck Depression Inventory
21-question multiple choice self-report inventory
Higher score, more depressed
Want to change this to a z-score
Above average --> positive z score
Below average --> negative z score
A score of 10 (-9 away from the mean)
Standard deviation =6
-9/6 = -1.5
Judging z-scores
ONLY if scores are normally distributed (perfect bell curve), 69% of the responses fall
within +/- 1 standard deviation of the mean and ~95% are within +/- 2 standard deviations
Different versions of Beck inventory
Can't really compare the two scores of different versions of the inventory
Convert to z-scores to compare
Cohen's d effect size
A z-score can provide a standardized summary of the mean difference
Null hypothesis - states prediction about the true population mean (the parameter)
Specified prior to the study and evaluated after collecting the sample data
o If null hypothesis true, the sample mean shouldn't be very different from hypothesis
o If null hypothesis false, the sample mean should be quite different from hypothesis
See if the data matches this prediction or if it refutes this prediction
Direction of Test (Alternate hypothesis)
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Document Summary

Standardized score scales: psychological variables (depression, narcissism) does not have inherent score scales, we make up the metrics, researchers use universal metrics. Iq scale: uses standard score scale with a mean of 100 and standard deviation of 15, the scale is completely made up. Mmpi: minnesota multiphasic personality inventory, widely used test of adult personality and psychopathology. T-scores: many psychological tests use a t-score scale with a mean of 50 and standard deviation of. Z-scores: a common standard score in psychology and statistics that uses a generic scale with a mean of 0 and standard deviation of 1, anything negative is below average. Importance of z-scores: any continuous variable can be converted to a z-score, can be used to describe scores, characterize difference between distributions. Judging z-scores: only if scores are normally distributed (perfect bell curve), 69% of the responses fall within +/- 1 standard deviation of the mean and ~95% are within +/- 2 standard deviations.

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