# PSYCH339 Lecture Notes - Lecture 4: Performance Appraisal, Discriminant Validity, Criterion Validity

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10 Aug 2016

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IQobserved = 187

What is his z-score?

Z= (187-100)/15

= 5.8

Sheldon has a higher IQ than 99.99% of other people

Approximate 4 out of

What is Sheldon’s true score?

Reliability: variance of the true score

IQbsereved = 187

Mean = 15

Rxx = 0.9

SEM = 15 sqrt 1-0.90

SEM = 4.74

95% CI = ~9.5 (4.74x2)

So Sheldon’s “true” IQ is probably between about 177.5 (187 – 9.5) and 196.5 (187 +

9.5)

Cont’d from last class

As a reliability gets higher, the 95% confidence interval goes down to the point

where you get to a perfect reliable test, there is no error so the true score is the

observe score

Can you have accuracy without being consistent? No

Can you have reliability without accuracy? No

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