WMS-IV
Wechsler Memory Scale - Fourth Edition
Overview of Contrast Scores
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Agenda
• Overview of Standard Scores
• Review of Traditional Discrepancy
Analyses
• Contrast Score Methodology
• Using Contrast Score Tables
• Contrast Score Interpretation
– Case Examples
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Standard Scores
• Norm Scores
– Individual scores are compared to a normative group
and establish a person’s ability in relation to others
– Norm scores are used to compare an individual to
same age peers
– Interpretation is straightforward, performance is
interpreted in relation to norm group
– Typically, adjustments are only made for age
– Performance is impaired in relation to same age peers
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Discrepancy Analyses
• Used to determine whether scores are
different from one another
• Assist in profile analysis
• Provides means of interpreting score
differences
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Simple-Difference Discrepancy
Analyses
• Used in WISC-IV, WAIS-IV and WMS-IV
• Obtain a difference by subtracting Score A from
Score B
• Compare the obtained difference using critical
values and base rates
– A critical value is the minimum required value of a
difference in order to obtain statistical significance
– The same critical values are used across ability levels
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Simple-Difference Discrepancy
Analyses
– Base rates are used to determine if a statistically
significant difference is rare and potentially clinically
significant
– Base rates are the frequency with which a specific
difference occurred in the normative sample
– Base rates are presented as percentages of the
overall sample or by ability level bands
– The less frequent the difference in the normative
sample, the more clinically relevant it is assumed to
be
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Predicted Difference
Discrepancy Analyses
• Used for WAIS-IV/WMS-IV Comparisons
• Uses regression methodology to create predicted scores
• Difference between predicted and actual scores are
compared with critical values and base rates
• Typically use linear regression techniques that assume a
constant rate of change across ability levels
• Typically tails of the distribution produce greater
variability in scores so linear techniques underestimate
differences at the tails and overestimate differences at
the middle range of ability
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Interpretation of Discrepancy
Analyses
• Difference between 2 scores is equal to or
greater than critical value (statistically significant)
– Johnny’s Working Memory Index and Verbal
Comprehension Index are statistically different at the
.05 level
• Base rates for the difference is 10.4 % in the
overall sample and 8.9% by ability level
– The difference occurs in 10.4% of the standardization
sample.
– The difference occurs in 8.9% of the standardization
sample at Johnny’s ability level.
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Contrast Score Overview
• Contrast scores yield new normative information on a
dependent measure, adjusting for the ability on the
control variable
– Contrast score name reflects which variable is control and which
is dependent
– Control variable is listed first in the score title and is used in
regression to create the contrast score
– Dependent measure is listed second in the title and the derived
contrast score reflects performance on this measure
• Examples
– Control vs. Dependent Contrast Scaled Score
– Auditory Attention vs. Response Set Contrast Scaled score
– Logical Memory Immediate Recall vs. Delayed Recall
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Contrast Score Overview
• Scored on 1-19 Scaled Score Metric
• Does not replace normative scores
• Answer’s specific hypothesis about an
examinee’s performance relative to their
performance on other measures
• Norm score asks: Is this person’s delayed
memory impaired?
• Contrast score asks: Is this person’s delayed
memory impaired given their initial encoding
ability?
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Using Contrast Score Tables
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Contrast Score Interpretation
• Higher scores indicate better than
expected performance on the dependent
score given performance on the control
score
– Delayed Memory is better than expected
given the examinee’s level of ability on
immediate memory
– Delayed Memory is superior when compared
to individuals of similar encoding ability
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Contrast Score Interpretation
• Low scores indicate poorer than expected
performance on the dependent score given
performance on the control score
– Delayed Memory is impaired given the examinee’s
level of ability on immediate memory
– Delayed Memory is impaired when compared to
individuals of similar encoding ability
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Contrast Score Interpretation
• Scores in the average range (8-12)
indicate no difference in performance
between the control and dependent
measures
– Performance on delayed memory is not
significantly different from ability on immediate
memory
– Delayed Memory performance is similar to
encoding ability
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• Example 1
Contrast Scores
Case Examples
– Normative Scores
• Joe obtains a 6 on VR I and a 6 on VR II
• Interpret VR I and VR II as impaired in comparison to his
same age peers
– Simple Difference Discrepancy Analysis
• VR I (6) – VR II (6) = 0
• Difference is not statistically significant
– Final Interpretation Using Simple Difference
• Both VR I and VR II are impaired but are not significantly
different from one another
– Suggested Intervention
• Target interventions toward both encoding and retrieval
deficits
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Contrast Scores
Case Examples
– Normative Scores
• Joe obtains a 6 on VR I and a 6 on VR II
– Contrast Score
• VR I vs. VR II Contrast Scaled Score is 8
– Final Interpretation Using Contrast Scaled Score
• In relation to his peers, both immediate and delayed memory
are impaired. Contrast score shows that VR Delayed is
actually within average (SS=8) when adjusted for his
immediate ability. His delayed memory performance is being
impacted by his immediate memory ability. Thus, his critical
memory problem may be in initial encoding ability.
– Suggested Intervention
• Target intervention toward encoding difficulties
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• Example 2
Contrast Scores
Case Examples
– Normative Scores
• Joe gets all items correct on recognition (>75%) and obtains
an 8 on LM II Delayed Recall
• Interpret Recognition as above average and LM II as average
in comparison to same age peers
– Simple Difference Discrepancy
• Can’t complete as both scores are not on same metric
– Final Interpretation Using Simple Difference
• Compared to same age-peers, recognition performance is
above average and delayed recall performance is average
– Suggested Intervention
• No intervention is needed
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Contrast Scores
Case Examples
– Normative Scores
• Joe gets all items correct on recognition (>75%) and obtains an 8 on
LM II Delayed Recall
– Contrast Score
• LM Recognition vs. LM II Contrast Scaled Score is 6
– Final Interpretation Using Contrast Scaled Score
• Compared to same age-peers, recognition performance is above
average and delayed recall performance is average. Contrast Score
demonstrates that recall is unexpectedly low for his recognition
ability. His performance appears to be impacted by his retrieval
ability. Thus, his critical memory problem may be in memory retrieval
or expressive language ability.
– Suggested Intervention
• Assess expressive language, target intervention toward retrieval
difficulties
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Contrast Scores
Case Examples
• Example 3 (General Ability vs. Delayed Memory)
– Normative Scores
• Joe obtains GAI of 120 and DMI of 100
• Interpret GAI of 120 as superior and DMI of 100 as average
– Simple Discrepancy Analysis
• GAI (120) – DMI (100) = 20
• Difference is statistically significant; base rate of 5-10%
– Final Interpretation Using Simple Difference
• DMI is significantly lower than GAI and a difference this large occurs
in less than 10% of the standardization sample. Both skills are
average compared to same age peers but delayed memory is
relatively weak in comparison to general cognitive ability
– Suggested Intervention
• If any intervention is needed, focus on delayed memory abilities
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Contrast Scores
Case Examples
– Normative Scores
• Joe obtains GAI of 120 and VMI of 100
– Contrast Score
• GAI vs. DMI Contrast Scaled Score is 7
– Final Interpretation Using Contrast Scaled
Score
• Contrast Score shows that his DMI score is low
average given his general cognitive ability.
– Suggested Intervention
• Target intervention on delayed memory abilities
Copyright © 2008 Pearson Education, inc. or its affiliates. All rights reserved.