# 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)

find more resources at oneclass.com

find more resources at oneclass.com

## 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.