lecture 5 - convergent and discriminant validity Flashcards
what is convergent validity
-give examples
If a measure has convergent validity then it correlates with (i.e., varies
with, is associated with) other measures of the same construct or with related constructs
So, for example, we would want a self-report depression scale to correlate highly with other self-report depression scales
- We would also want it to correlate with ratings of depression obtained by other methods
- For example, we would want it to correlate highly with clinicians’ ratings of depression
So, if we gave the scale to a sample of patients and also had clinicians
interview them, we could look at the relationship between scores from the two methods..
how can we examine the convergent validity of a self report depression scale
a scatterplot which can be used to examine the relationship
between two variables; here they are (1) a clinician’s rating of patients’
depression, and (2) the self-report scores of the patients
-look at plot on slides
Suppose we have 12 patients
(patients A to L)
In this example convergent
validity is high: there is a high
level of agreement (correlation)
between the scale and the
ratings
most psychological tests have ______ convergent validity
-give examples
Most psychological tests have decent convergent validity (they wouldn’t be used otherwise)
- For example, most verbal memory scales correlate highly with each other
- Similarly, most depression scales correlate highly with each other, and with clinician ratings of depression
sometimes construct variance is swamped by _______ variance
explain
method
Sometimes construct variance (the thing we want to measure) is swamped by method variance (the way we have measured it
When method variance swamps construct variance, it means that the differences observed in the data are more a result of the measurement methods rather than the true differences in the construct itself. This can lead to misleading conclusions about the construct being studied.
example of construct variance being swamped by method variance
cole 1987
Cole’s (1987) analysis of patient and child ratings of the child’s level of depression…
Can be seen that there is good agreement across different scales when the children rated their
own level of depression
- There is also good agreement across the same scales when the mothers rated their childs’ level
of depression - However, there is very poor agreement between the two different methods of assessment
(the correlation is only 0.15)
what is discriminant validity
-give an example
Discriminant validity is the flip side of convergent validity: if a measure
has good discriminant validity then it does not correlate with (is not
associated with) measures it should be unrelated to, or weakly related to
- Take the example of a test / exam of (say) geographical knowledge
- Suppose the test correlates highly with writing speed: then it has poor
discriminant validity - The test is supposed to be measuring geographical knowledge, not the ability to write fast
a ______ correlation with an unrelated measure indicates low or poor discriminant validity
a high correlation with an unrelated measure indicates low
or poor discriminant validity
discriminant validity example
-depression scales and social desirability
As another example, Depression scales correlate very highly (-0.9) with measures of social desirability (Langevin & Stanger, 1979)
- Social desirability scales are supposed to measure the extent to which people attempt to present themselves to others in an overly positive light
- Example item: “There have been occasions when I took advantage of someone”
- Depression scales tend to correlate highly with social desirability (high depression is associated with low social desirability scores – i.e., they are
negatively correlated
depression scales tend to correlate ______ with social desirability
Depression scales tend to correlate highly with social desirability (high
depression is associated with low social desirability scores – i.e., they are negatively correlated)
what is the locus of the problem with the discriminant validity of the depression and social desirability scales?
Is the problem with depression
scales, or with social desirability scales?
- The problem is probably largely with the social desirability scales
- Social desirability scales are supposed to measure the extent to which people portray themselves to others in an overly positive light
- But it appears they may also be measuring our ability to portray ourselves to ourselves in an overly positive light
how do social desirability scales have poor discriminant reliability
these scales are designed to measure the extent to which people present themselves in a socially favourable manner. However, because non-depressed individuals may inflate their self-views (due to the “rose-tinted spectacles”), they could score higher on social desirability scales. Meanwhile, depressed individuals may score lower because they view themselves more realistically or negatively.
Poor Discriminant Validity: This refers to the idea that the social desirability scale struggles to effectively distinguish between different psychological states or traits (like self-esteem versus actual personality traits). Because both groups (non-depressed and depressed) can interpret and respond to social desirability items differently, it makes it challenging to draw clear conclusions about what the scale is measuring
do anxiety and depression scales have good convergent validity
Anxiety and depression scales generally have good convergent validity (i.e., anxiety scales correlate highly with each other, and with clinician’s ratings; same
goes for depression scales)
Can Self-Report Scales Differentiate Between Anxiety and Depression?
(-discriminant validity between anx and dep scales
how well do they perform in terms of discriminant validity?
Not well at all!
The anxiety scales have good convergent validity, as do the depression scales
However, the anxiety and depression scales have very poor discriminant validity: the correlation between anxiety & depression factors is not significantly different from 1.0
Can Self-Report Scales Differentiate Between Anxiety and Depression?
-between construct correlations often exceed within construct correlations
It is not at all uncommon for an anxiety scale to correlate more highly with a depression scale than it does with another anxiety scale (same goes for depression scales)
Formal way of saying that: between-construct correlations often exceed within- construct correlations
Informal way: You think you are measuring anxiety but in fact looks like you may be measuring depression and vice-versa
what is the cause for the poor discriminant validity between anxiety and depression scales ?
-is the problem the scales or the constructs?
Note: it is not just self-report scales that have this problem: also happens with clinician’s ratings
-There certainly is a good deal of genuine overlap between anxiety and depression so we would expect a correlation between scales
However, it should still be possible to differentiate them
-tripartite theory : negative affectivity
