1. Looking at the both ‘ends’ of the social aptitude dimension
Esse aspecto é central para a psiquiatria.
Giovanni Abrahão Salum, MD PhD
Department of Psychiatry
Universidade Federal do Rio Grande do Sul

2. OUTLINE Measurement in Psychiatry
How can Item Response Theory (IRT) help measurement development in psychiatry?
Looking at the both ends of the Social Aptitude Dimension

3. RELIABILITY
VALIDITY
MECHANISMS

4. Dimensions or categories
MEASUREMENT
Population
Social Aptitudes
Empirical Phenomena
CATEGORIZATION
Dimensions or categories
Mathematical Structure

5. MEASUREMENT The dichotomous approach Population Classification
No Mental Illness
Mentall Illness

6. MEASUREMENT The ordinal approach < < Population Classification
No Mental Illness
Subth
No Symptoms
<
Mild
Mod
Sev
<
Mental Illness

7. MEASUREMENT The continuous approach Population
In between two positions lies a third that can be instantiated
There are no gaps in the continuum

8. MEASURING WHAT WE CANNOT SEE
DIRECT MEASURES
INDIRECT MEASURES
Social Aptitudes
Can take the lead without seeming bossy
Can apologize and resolve matters to avoid hard feelings
A good loser
Easy to chat with
Aware of what is socially appropriate
Categorical
indicators
Continuous
trait

9. vs. ITEM RESPONSE THEORY
CLASSICAL TEST THEORY
vs. ITEM RESPONSE THEORY
Classical Test Theory
A test is comprised of a “true” value, plus randomized error
Item level statistics
Discrimination: item-total correlation
Difficulty: % answered incorrectly
Test level statistics
Reliability: Cronbach’s
Highly dependent on the sample
Summed scores
Item Response Theory
Measure the underlying ability (or trait) which is producing the test performance
Item level statistics
Discrimination (a parameter)
Location (b parameter)
Item characteristic curve
Test level statistics
Test Information Function
Less dependent on the sample
IRT-based scores
xobs = xtrue + G(0, err)

10. ITEM RESPONSE THEORY 2-parameter model
Discrimination (slope, a parameter)
How well an item discriminates subjects
How related an indicator is to the latent trait (the item-total correlation)
Difficulty (threshold, b parameter)
Where in the latent trait the item concentrates ability to discriminate
How much latent trait “is needed” to endorse items

11. METHODS
Unipolar scales (example)

12. METHODS
The Social Aptitudes Scale

13. Measures or quasi traits
MEASUREMENT CONTINUUM
Unipolar (quasi-trait) vs. Bipolar
Unipolar
Measures or quasi traits
No symptoms
Several symptoms
Captures variability at
the end of the continuum
Above average
Bipolar
measures
Average
Bellow average
Captures variability at both ends of the continuum

14. HIGH RISK COHORT STUDY
FOR PSYCHIATRIC DISORDERS (HRC)

15. RESULTS
Histogram of summed scores

16. RESULTS
Test Information Function

17. RESULTS
Item Information Curves

18. RESULTS
Item Characteristic Curves

19. MEASUREMENT Quantile Regression Correlation coefficient (r)
Quantiles of SAS

20. ADHD Rating Scales
Conners, SDQ-C, SDQ-P and SWAN

21. Measures or quasi traits
MEASUREMENT CONTINUUM
Unipolar (quasi-trait) vs. Bipolar
Unipolar
Measures or quasi traits
No symptoms
Several symptoms
Captures variability at
the end of the continuum
Above average
Bipolar
measures
Average
Bellow average
Captures variability at both ends of the continuum

22. CONCLUSIONS
Social Aptitude Scale captures information about the full social aptitude trait
Unipolar measures might be optimal to discriminate clinical from non-clinical samples and characterize severity among clinical samples, but might not be sensitive to discriminate subjects in the community
Bipolar measures might offer the possibility to measure both strengths and weaknesses and provide information about the full spectrum of a psychiatric trait

23.
OBRIGADO!