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

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

RELIABILITY VALIDITY MECHANISMS

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

MEASUREMENT The dichotomous approach Population Classification No Mental Illness Mentall Illness

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

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

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

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)

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

METHODS Unipolar scales (example)

METHODS The Social Aptitudes Scale -2 -1 0 1 2

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

HIGH RISK COHORT STUDY FOR PSYCHIATRIC DISORDERS (HRC)

RESULTS Histogram of summed scores

RESULTS Test Information Function

RESULTS Item Information Curves

RESULTS Item Characteristic Curves

MEASUREMENT Quantile Regression Correlation coefficient (r) Quantiles of SAS

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

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

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

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