Br. J. clin. Pharmac. (1976), Supplement, 61-67
THE COMPARATIVE VALUE OF TYPES OF RATING SCALE R.F. GARSIDE Department of Psychological Medicine, The Royal Victoria Infirmary, Queen Victoria Road, Newcastle upon Tyne
There are four main types of rating scales which may be useful in psychiatry. The first may be called assessment or descriptive scales and are used to assess the degree of psychiatric illness, such as depression. The second type of scale is discriminatory rather than descriptive. It may be useful in attempting to arrive at a differential diagnosis. The third and fourth types are predictive, rather than descriptive. These kinds of scale may be useful in predicting the course and outcome of particular psychiatric conditions or the results of specific treatments. I consider these four types of scales in order.
Individual scales, such as Hamilton's, make no attempt to arrive at a diagnosis. Indeed, a diagnosis is usually made before using such a scale. Such individual scales are mainly used to evaluate the effects of various forms of treatment. Multiple scales, however, such as Wittenborn's (1955), provide descriptions or measurements along several different dimensions and at the same time. The patient's pattern of score can therefore be used as a diagnostic aid. If he scores highest along a certain dimension, this is naturally suggestive of the corresponding diagnosis. But it must be remembered that the dimensions of such multiple scales are usually not negatively correlated. Thus it may be that a particular patient may score higher in two or more dimensions-such as 'depressive retardation', 'anxiety' and 'intellectual impairment'. The use of such multiple scales for diagnostic purposes therefore presupposes acceptance of the idea of multiple diagnoses.
Descriptive scale An assessment or descriptive scale, such as the Hamilton rating scale for primary depressive illness (Hamilton, 1960, 1967), is used to assess and thus to describe patients with reference to a certain defined psychiatric dimension, such as depressive illness, or to certain personality factors, such as neuroticism. Such scales are not primarily concerned with arriving at a diagnosis, although as I shall indicate later, a collection of such scales such as those of Wittenborn (1955, 1962), considered together, may be relevant to
Diferential scales However, there are some scales which have been designed specifically to assist in arriving at a differential diagnosis. For example, the symptom-sign inventory (Foulds & Hope, 1968) can be used to differentiate between psychotics and neurotics. The Newcastle diagnostic index (Carney et al., 1965) has been used to attempt to differentiate between those depressed patients who are psychotic (or endogenous) rather than neurotic and vice versa (Kendell, 1968; Noble & Lader, 1972; Post, 1972). In order to indicate the essential difference between descriptive or assessment scales on the one hand and diagnostic or discriminating scales on the other, I want to consider some data regarding the Newcastle diagnostic index. Table 1 shows the factor loadings of 35 features considered by Carney et al. (1965). The first factor is bipolar; it has large negative as well as large positive loadings. This factor accounts for 20% of the variance. This factor clearly differentiates between those features which are psychotic (or endogenous) and those which are mainly neurotic. The next most important factor (which accounts for 6% of the variance) is one of general depression. The three features with non-trivial negative loadings are age, adequate personality and hopeful outlook, which
diagnosis. A descriptive scale should, of course, measure what it is intended to measure. To ascertain whether this is so, a factor or component analysis may be carried out to see whether a general or common factor emerges from the data. If the separate items seem by their clinical nature to measure the dimension or illness in question and, further, if an important general factor exists, then such a general factor must measure the dimension or illness in question. The existence of an important general factor indicates that it is clinically meaningful to describe patients along the factor or dimension in question. For example, Hamilton's depression scale has a general factor which accounts for more than one-fifth of the total variance; it is therefore important. It is a general factor because, for men, there are no nontrivial negative factor loadings, and in the case of women, only one such loading out of 17 (Hamilton, 1967). Thus it may be concluded that (a) it is clinically meaningful to describe patients along a dimension of general primary depressive illness; and (b) the degree of such illness is indicated by the number of symptoms present and by their severity. 61
R.F. GARSIDE
62
could equally well be youth, inadequate personality and hoepless outlook, and then could sensibly have positive loadings. Figure 1 is a diagrammatic representation of the data of Table 1. It is clear that there are two groups of features forming a psychotic cluster and a neurotic cluster. The loadings along the horizontal discriminating dimension (or factor) are very similar to the correlations with diagnosis (see Table 1), and therefore the clinical differential diagnosis is validated by the factor analysis. The differential diagnosis was therefore used to construct a differentiating scale including the 18 items named in Figure 1. The scale is much the same as the differentiating, horizontal dimension in Figure 1, but is probably a more efficient discrimination than the factor. Table 1
Note that the discriminating, horizontal dimension is not descriptive. It does not pass through either centre of clusters of features. Thus the dimension or scale cannot, by itself, be used to describe patients. Distance along this dimension, for example, cannot indicate the severity of depression. It is the vertical, general factor which measures the severity of depression in terms of the number of symptoms. This general factor could, therefore, be used to describe patients in terms of the severity of their depression-like the Hamilton scale. This is because this vertical dimension passes near the centre of all 35 depressive features. But the point is that this descriptive, general factor of depression is independent and uncorrelated with the discriminating factors. Thus descriptive scales-which are analogous to general
Factor loadings, diagnosis and ECT outcome correlations (decimal points omitted) Factor loadings (N= 129)
Correlations with
Diagnosis
ECT outcome
(6 months) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35.
Age (40 +) No precipitants Adequate personality No adequate psychogenesis Unvarying depression No reactivity Distinct quality of depression Weight loss (3.2 kg +) Constipation Pyknic Previous episodes Family history endog. dep. Early waking Worse a.m. Depressive psychomotor activity Anxiety Delusion of retribution Nihilistic delusions Somatic delusions Paranoid delusions Suicidal rumination/attempt Depressive hallucinations History over one year Family history-neurosis Worse p.m. Blames others Self pity Hopeful patient's attitude Hypochondriasis Neurotically suicidal Irritable Phobias Hysteria Initial insomnia Guilt
I
II
IlIl
209 348 385 505 572 568 420 362 138 186 486 164 227 060 736 -686 591 673 313 446 225 400 -608 -186 -276 -450 -554 -672 -616 -394 -473 -442 -354 -308 673
-458 065 -381 -014 212 301 098 -071 -083 273 005 294 124 267 053 212 112 305 173 276 358 275 000 326 021 430 081 -399 152 257 384 458 233 161 000
-167 -179 051 -218 -203 -187 146 117 059 -223 -264 -182 -207 -694 -023 -117 441 063 184 410 -103 394 208 047 -580 219
-278 -032 -041 091 -043 -048 -036 219 132
N=1116
202 393 419 534 534 565 425 433 270 263 459 155 271 143 675 -619 470 657 317 381 257 354 -493 -179 -265 -439 -486 -652 -483 -341 -371 -338 -312 -356 611
N=108 218 236 234 315 261 303 155 395 043 249 413 113 270 065 440 -458 250 384 284 206 139 172 -433 -103 -252 -395 -274 -358 -497 -332 -255 -258 -325 -012 392
63
THE COMPARATIVE VALUE OF TYPES OF RATING SCALE
Depressive psychomotor act.(
episodes \f guilt , .
-.8
-.7
.
-.6 -.5 -.4
Figure 1
*Anxiety * Hypochondriacal
orse P-m.
-.2
Adequate psychogenesis + N')
L
~W .lo. -.3
)
(
Hysterical.
I1
2
Distinct quality *
Delusion
- (P1)
others
/Inad. pers..o
t Paranoid (i) delusions 3 *(0) Pykni.c 3)A. Earlywakening .2 }343 *Somatic | \ delusions
/E) \ Nihilistic delusions * ( i) / \
-.1
..ss.
.2
.1
0
.
.6
.5
.4
.3
.7
.8
Diagrammatic representation of data in Table 1
factors-are quite dissimilar from discriminating scales-which are analogous to bipolar, differentiating, factors. If lines were drawn through the centres of the two clusters, as shown in Figure 1, then the distances along these two lines could be used to describe patients. The distances along the neurotic dimension (N) would measure the extent to which a patient was neurotically depressed. The distances along the psychotic dimension (P) the extent to which he was psychotically depressed. Note that the angle between the N and P lines is 1300, which corresponds to a correlation of 0.64 between the syndromes of neurotic and psychotic depression in Carney's material. Fahy et al. (1969) found a similar correlation of -0.63. These correlations do not, of course, mean that the two conditions are mutually exclusive; some patients will show symptoms of both disorders. Kendell (1968) found that the two conditions were virtually independent-that is the correlations between them were not negative, as shown in Figure 2. This gives Kendell's third analysis which generated two dimensions-psychotic and neurotic depression. These dimensions are at right angles, and if they are rotated through 450, one becomes general and one becomes differentiating. Once again, distance along the differentiating dimensions would provide some evidence as to whether the patient was mainly neurotic or mainly psychotic, but would not indicate how depressed the patient was. It is the other, general dimension, which would measure general depresssion and this dimension is therefore descriptive in a general sense. But the distances along Kendell's original dimension are descriptive in a more specific sense. Both these dimensions are meaningful in a descriptive
p 0.6 0.5 05(P)/ 30 0.4 0.3
31
*
33
36 241 39 26 2 341920
12 /
0.1 -0.2
4 2823 3216
\
7
N
5653
-
-
27-
25 2221037
Factor1 38
-
,~~~/14/
\
0.1 11
4
41°
1
0.3
-Q4 + (N) Factor 2 0.1 0.2 0.3 0.4 0.5 0.6 -0.5 -0.4-0.3-Q2-0.1 Figure 2
sense. But a patient's score along both should be given if a reasonably adequate description of the patient is to be attained. This description would indicate whether, and to what extent, the patient was psychotically depressed. and to what extent he was neurotically depressed. Note that these two aspects of the patient, according to Kendell's data, are quite independent. This means that a patient's scores along one dimension provide no information as to his score on the other. Thus Kendell's results suggest that it would be useful to have two descriptive scales of depression-one measuring psychotic depression and the other measuring neurotic depression. This suggestion implies no criticism of Hamilton's scale, which measures general depression. For,
64
R.F. GARSIDE 32
The Newcastle diagnostic scale has been used both by Kendell and by Post. They have recently (1973) combined their results, giving a total of 271 patients. The distribution of these patients' scores are seen in Figure 3. There has been some controversy as to whether this distribution indicates that patients can be placed in diagnostic categories, but nevertheless it is clear that the scale spreads patients out, and moreover one end corresponds to psychotic depression, whereas the other end corresponds to neurotic depression. But this scale does not provide any information as to the degree of depression; it is purely discriminatory.
28 24>- 20:3
1612 8 4
-3-2 -10 1 2 3 4 5 6 7 8 9 10 111213
Score Figure 3 Scores of Maudsley cases on Newcastle diagnostic index.
although there are two distinct kinds of intelligence-verbal and practical-it is nevertheless sensible and common practice to measure general intelligence.
Table 2
Predictive scale-course and outcome Another kind of scale is that which is designed to predict something-that is, the course and outcome of some psychiatric disorder. Such predictive scales are quite different from descriptive scales. The items of a descriptive scale should correlate higher among themselves, because they should all measure the same attribute. But, on the contrary, the items of a predictive scale should correlate with that which is
Features correlating with outcome in affective disorders (P
THE COMPARATIVE VALUE OF TYPES OF RATING SCALE R.F. GARSIDE Department of Psychological Medicine, The Royal Victoria Infirmary, Queen Victoria Road, Newcastle upon Tyne
There are four main types of rating scales which may be useful in psychiatry. The first may be called assessment or descriptive scales and are used to assess the degree of psychiatric illness, such as depression. The second type of scale is discriminatory rather than descriptive. It may be useful in attempting to arrive at a differential diagnosis. The third and fourth types are predictive, rather than descriptive. These kinds of scale may be useful in predicting the course and outcome of particular psychiatric conditions or the results of specific treatments. I consider these four types of scales in order.
Individual scales, such as Hamilton's, make no attempt to arrive at a diagnosis. Indeed, a diagnosis is usually made before using such a scale. Such individual scales are mainly used to evaluate the effects of various forms of treatment. Multiple scales, however, such as Wittenborn's (1955), provide descriptions or measurements along several different dimensions and at the same time. The patient's pattern of score can therefore be used as a diagnostic aid. If he scores highest along a certain dimension, this is naturally suggestive of the corresponding diagnosis. But it must be remembered that the dimensions of such multiple scales are usually not negatively correlated. Thus it may be that a particular patient may score higher in two or more dimensions-such as 'depressive retardation', 'anxiety' and 'intellectual impairment'. The use of such multiple scales for diagnostic purposes therefore presupposes acceptance of the idea of multiple diagnoses.
Descriptive scale An assessment or descriptive scale, such as the Hamilton rating scale for primary depressive illness (Hamilton, 1960, 1967), is used to assess and thus to describe patients with reference to a certain defined psychiatric dimension, such as depressive illness, or to certain personality factors, such as neuroticism. Such scales are not primarily concerned with arriving at a diagnosis, although as I shall indicate later, a collection of such scales such as those of Wittenborn (1955, 1962), considered together, may be relevant to
Diferential scales However, there are some scales which have been designed specifically to assist in arriving at a differential diagnosis. For example, the symptom-sign inventory (Foulds & Hope, 1968) can be used to differentiate between psychotics and neurotics. The Newcastle diagnostic index (Carney et al., 1965) has been used to attempt to differentiate between those depressed patients who are psychotic (or endogenous) rather than neurotic and vice versa (Kendell, 1968; Noble & Lader, 1972; Post, 1972). In order to indicate the essential difference between descriptive or assessment scales on the one hand and diagnostic or discriminating scales on the other, I want to consider some data regarding the Newcastle diagnostic index. Table 1 shows the factor loadings of 35 features considered by Carney et al. (1965). The first factor is bipolar; it has large negative as well as large positive loadings. This factor accounts for 20% of the variance. This factor clearly differentiates between those features which are psychotic (or endogenous) and those which are mainly neurotic. The next most important factor (which accounts for 6% of the variance) is one of general depression. The three features with non-trivial negative loadings are age, adequate personality and hopeful outlook, which
diagnosis. A descriptive scale should, of course, measure what it is intended to measure. To ascertain whether this is so, a factor or component analysis may be carried out to see whether a general or common factor emerges from the data. If the separate items seem by their clinical nature to measure the dimension or illness in question and, further, if an important general factor exists, then such a general factor must measure the dimension or illness in question. The existence of an important general factor indicates that it is clinically meaningful to describe patients along the factor or dimension in question. For example, Hamilton's depression scale has a general factor which accounts for more than one-fifth of the total variance; it is therefore important. It is a general factor because, for men, there are no nontrivial negative factor loadings, and in the case of women, only one such loading out of 17 (Hamilton, 1967). Thus it may be concluded that (a) it is clinically meaningful to describe patients along a dimension of general primary depressive illness; and (b) the degree of such illness is indicated by the number of symptoms present and by their severity. 61
R.F. GARSIDE
62
could equally well be youth, inadequate personality and hoepless outlook, and then could sensibly have positive loadings. Figure 1 is a diagrammatic representation of the data of Table 1. It is clear that there are two groups of features forming a psychotic cluster and a neurotic cluster. The loadings along the horizontal discriminating dimension (or factor) are very similar to the correlations with diagnosis (see Table 1), and therefore the clinical differential diagnosis is validated by the factor analysis. The differential diagnosis was therefore used to construct a differentiating scale including the 18 items named in Figure 1. The scale is much the same as the differentiating, horizontal dimension in Figure 1, but is probably a more efficient discrimination than the factor. Table 1
Note that the discriminating, horizontal dimension is not descriptive. It does not pass through either centre of clusters of features. Thus the dimension or scale cannot, by itself, be used to describe patients. Distance along this dimension, for example, cannot indicate the severity of depression. It is the vertical, general factor which measures the severity of depression in terms of the number of symptoms. This general factor could, therefore, be used to describe patients in terms of the severity of their depression-like the Hamilton scale. This is because this vertical dimension passes near the centre of all 35 depressive features. But the point is that this descriptive, general factor of depression is independent and uncorrelated with the discriminating factors. Thus descriptive scales-which are analogous to general
Factor loadings, diagnosis and ECT outcome correlations (decimal points omitted) Factor loadings (N= 129)
Correlations with
Diagnosis
ECT outcome
(6 months) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35.
Age (40 +) No precipitants Adequate personality No adequate psychogenesis Unvarying depression No reactivity Distinct quality of depression Weight loss (3.2 kg +) Constipation Pyknic Previous episodes Family history endog. dep. Early waking Worse a.m. Depressive psychomotor activity Anxiety Delusion of retribution Nihilistic delusions Somatic delusions Paranoid delusions Suicidal rumination/attempt Depressive hallucinations History over one year Family history-neurosis Worse p.m. Blames others Self pity Hopeful patient's attitude Hypochondriasis Neurotically suicidal Irritable Phobias Hysteria Initial insomnia Guilt
I
II
IlIl
209 348 385 505 572 568 420 362 138 186 486 164 227 060 736 -686 591 673 313 446 225 400 -608 -186 -276 -450 -554 -672 -616 -394 -473 -442 -354 -308 673
-458 065 -381 -014 212 301 098 -071 -083 273 005 294 124 267 053 212 112 305 173 276 358 275 000 326 021 430 081 -399 152 257 384 458 233 161 000
-167 -179 051 -218 -203 -187 146 117 059 -223 -264 -182 -207 -694 -023 -117 441 063 184 410 -103 394 208 047 -580 219
-278 -032 -041 091 -043 -048 -036 219 132
N=1116
202 393 419 534 534 565 425 433 270 263 459 155 271 143 675 -619 470 657 317 381 257 354 -493 -179 -265 -439 -486 -652 -483 -341 -371 -338 -312 -356 611
N=108 218 236 234 315 261 303 155 395 043 249 413 113 270 065 440 -458 250 384 284 206 139 172 -433 -103 -252 -395 -274 -358 -497 -332 -255 -258 -325 -012 392
63
THE COMPARATIVE VALUE OF TYPES OF RATING SCALE
Depressive psychomotor act.(
episodes \f guilt , .
-.8
-.7
.
-.6 -.5 -.4
Figure 1
*Anxiety * Hypochondriacal
orse P-m.
-.2
Adequate psychogenesis + N')
L
~W .lo. -.3
)
(
Hysterical.
I1
2
Distinct quality *
Delusion
- (P1)
others
/Inad. pers..o
t Paranoid (i) delusions 3 *(0) Pykni.c 3)A. Earlywakening .2 }343 *Somatic | \ delusions
/E) \ Nihilistic delusions * ( i) / \
-.1
..ss.
.2
.1
0
.
.6
.5
.4
.3
.7
.8
Diagrammatic representation of data in Table 1
factors-are quite dissimilar from discriminating scales-which are analogous to bipolar, differentiating, factors. If lines were drawn through the centres of the two clusters, as shown in Figure 1, then the distances along these two lines could be used to describe patients. The distances along the neurotic dimension (N) would measure the extent to which a patient was neurotically depressed. The distances along the psychotic dimension (P) the extent to which he was psychotically depressed. Note that the angle between the N and P lines is 1300, which corresponds to a correlation of 0.64 between the syndromes of neurotic and psychotic depression in Carney's material. Fahy et al. (1969) found a similar correlation of -0.63. These correlations do not, of course, mean that the two conditions are mutually exclusive; some patients will show symptoms of both disorders. Kendell (1968) found that the two conditions were virtually independent-that is the correlations between them were not negative, as shown in Figure 2. This gives Kendell's third analysis which generated two dimensions-psychotic and neurotic depression. These dimensions are at right angles, and if they are rotated through 450, one becomes general and one becomes differentiating. Once again, distance along the differentiating dimensions would provide some evidence as to whether the patient was mainly neurotic or mainly psychotic, but would not indicate how depressed the patient was. It is the other, general dimension, which would measure general depresssion and this dimension is therefore descriptive in a general sense. But the distances along Kendell's original dimension are descriptive in a more specific sense. Both these dimensions are meaningful in a descriptive
p 0.6 0.5 05(P)/ 30 0.4 0.3
31
*
33
36 241 39 26 2 341920
12 /
0.1 -0.2
4 2823 3216
\
7
N
5653
-
-
27-
25 2221037
Factor1 38
-
,~~~/14/
\
0.1 11
4
41°
1
0.3
-Q4 + (N) Factor 2 0.1 0.2 0.3 0.4 0.5 0.6 -0.5 -0.4-0.3-Q2-0.1 Figure 2
sense. But a patient's score along both should be given if a reasonably adequate description of the patient is to be attained. This description would indicate whether, and to what extent, the patient was psychotically depressed. and to what extent he was neurotically depressed. Note that these two aspects of the patient, according to Kendell's data, are quite independent. This means that a patient's scores along one dimension provide no information as to his score on the other. Thus Kendell's results suggest that it would be useful to have two descriptive scales of depression-one measuring psychotic depression and the other measuring neurotic depression. This suggestion implies no criticism of Hamilton's scale, which measures general depression. For,
64
R.F. GARSIDE 32
The Newcastle diagnostic scale has been used both by Kendell and by Post. They have recently (1973) combined their results, giving a total of 271 patients. The distribution of these patients' scores are seen in Figure 3. There has been some controversy as to whether this distribution indicates that patients can be placed in diagnostic categories, but nevertheless it is clear that the scale spreads patients out, and moreover one end corresponds to psychotic depression, whereas the other end corresponds to neurotic depression. But this scale does not provide any information as to the degree of depression; it is purely discriminatory.
28 24>- 20:3
1612 8 4
-3-2 -10 1 2 3 4 5 6 7 8 9 10 111213
Score Figure 3 Scores of Maudsley cases on Newcastle diagnostic index.
although there are two distinct kinds of intelligence-verbal and practical-it is nevertheless sensible and common practice to measure general intelligence.
Table 2
Predictive scale-course and outcome Another kind of scale is that which is designed to predict something-that is, the course and outcome of some psychiatric disorder. Such predictive scales are quite different from descriptive scales. The items of a descriptive scale should correlate higher among themselves, because they should all measure the same attribute. But, on the contrary, the items of a predictive scale should correlate with that which is
Features correlating with outcome in affective disorders (P
