lecture 5- convergent and discriminant validity Flashcards
1
Q
convergent validity
A
- 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…
2
Q
convergent validity cont.
A
- 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
- However, high convergent validity is not always found
- Sometimes construct variance (the thing we want to measure) is swamped by method variance (the way we have measured it)
- A dramatic example is provided by Cole’s (1987) analysis of patient and child
ratings of the child’s level of depression…
3
Q
cole, 1987
A
- 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)
4
Q
what is discriminant validity?
A
- 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
- To be clear: a high correlation with an unrelated measure indicates low
or poor discriminant validity
5
Q
discriminant validity cont.2
A
- 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)
6
Q
discriminant validity cont.3
A
- Therefore there is a problem with the discriminant validity of these scales
- But what is the locus of the problem? 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
7
Q
discriminant validity contd.4
A
- In other words the non-depressed wear rose-tinted spectacles – they protect their self-esteem / mood by seeing themselves in an overly positive light
- In contrast, depressed people do not (depressive realism) and indeed devalue themselves
- Thus, social desirability scales appear to have poor discriminant validity
8
Q
Can Self-Report Scales Differentiate Between Anxiety and Depression?
A
- 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)
- (The earlier example of mother and child ratings is an exception to this rule)
However, how well do they perform in terms of discriminant validity?
-Not well at all!
9
Q
Can Self-Report Scales Differentiate Between Anxiety and Depression? cont2
A
- 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
10
Q
Can Self-Report Scales Differentiate Between Anxiety and Depression? cont 3
A
Why should that happen?
- Note: it is not just self-report scales that have this problem: also happens with
clinician’s ratings
Is the problem with the scales or with the constructs?
- 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
Clark & Watson (1991,1995 etc) in a series of influential papers introduced tripartite
theory
This theory proposes that anxiety and depression share a common feature: negative
affectivity
11
Q
what does negative affectivity (NA) refer to?
A
Negative affectivity (NA) refers to unpleasant engagement i.e., feeling “distressed”,
“scared”, “upset”, “irritable”
12
Q
what do Clark and Watson argue?
A
- Clark & Watson argue that most anxiety and depression scales predominantly measure negative affectivity, rather than anything specific to anxiety and depression
- It is argued this is why anxiety and depression scales have poor discriminant validity
- Tripartite theory proposes that there are specific components to anxiety and
depression that allow them to be differentiated…
13
Q
low positive affect
A
- The proposed specific component for depression is low positive affect : that is the
absence of feeling such as “enthusiasm”, “interest”, “alertness” - Low positive affect is very similar to the psychiatric concept of anhedonia (“loss-of-
pleasure”) - It is suggested that someone who is suffering from anxiety does not necessarily have low positive affect: they can still enjoy some things
- In contrast, the severely depressed person gets no pleasure (and has little or no
interest) in anything - The proposed specific component for anxiety is physiological hyperarousal
14
Q
according to tripartite theory
A
- both anxious and depressed individuals will be high on negative affectivity
- Depressed people will (in addition to high NA) have low positive affect
- Anxious individuals will (in addition to high NA) be high on physiological hyperarousal
Note: “anxious arousal” is used as a synonym for physiological hyperarousal
15
Q
the MASQ
A
- Tripartite theory suggests that, if self-report depression scales targeted (low) positive affect, and anxiety scales targeted anxious arousal, we would get round the problem of very poor discriminant validity
- Clark & Watson have come up with a candidate scale: the Mood and Anxiety
Symptom Questionnaire (MASQ) - Has an Anhedonic Depression scale: this should measure the specific component
of depression
Also has an Anxious Arousal scale: this should measure the specific component of
anxiety
