CAMCOG: Detaileddescription, population dataand psychometric properties

CAMCOG: Detailed description, population dataand psychometric properties

The Cambridge Cognitive Examination (CAMCOG) is aconcise neuropsychological test for the assessment ofcognitive impairment in elderly people. It was designedspecifically to assist in the diagnosis of dementia at anearly stage. CAMCOG assesses a broad range of cogni-tive functions, as is required for the diagnosis of demen-tia, and it minimises floor and ceiling effects by coveringa range of item difficulty.

Aims

● To assess the range of cognitive functions requiredfor a diagnosis of dementia.

● To assist in differential diagnosis within the demen-tias.

● To incorporate items which are graded in difficultywithin a cognitive domain in order to assess the fullrange of cognitive ability.

● To permit the measurement of cognitive declinefrom very high levels of premorbid ability by minimiz-ing ceiling effects.

● To facilitate comparison with some other widelyused brief cognitive tests, by including them withinits framework.

● To examine profiles of cognitive performance byderiving scores on subscales which assess differentcognitive abilities.

Content

The items contained in the CAMCOG were selected tosample the areas of cognitive functioning which arespecified in operational diagnostic criteria, such as thoseelaborated in DSM-IV (American Psychiatric Association,1994) and ICD-10 (World Health Organization, 1993).These cognitive functions include memory, language,attention, perception, praxis and thinking (now calledexecutive functioning). The CAMCOG also samplesimportant domains within an area of cognitive function-ing; for example, memory items include assessment ofremote and recent memory, semantic and episodicmemory, intentional and incidental learning, and recalland recognition measures of retrieval. The CAMCOGincorporates items which are commonly used in neu-ropsychological assessment to examine dissociable fun-tions. Thus, for example, there are measures of languagecomprehension and language expression and these are

assessed both in an oral and in a written form. Somestandard neuropsychological items which are included inthe CAMCOG are verbal fluency, similarities and theidentification of objects photographed from unusualviews. A summary of CAMCOG items and subscales isprovided in Table 1.

All the MMSE items are included in the cognitive exami-nation but the following are not used in calculating theCAMCOG score; naming two objects (pencil, wrist-watch), registration and recall of three words, writing asentence and paper folding. The processes involved inthese tests are assessed in more detail by otherCAMCOG items. CAMCOG also contains theAbbreviated Mental Test (AMT) of Hodkinson (1972),derived from the original Dementia Scale of Blessedet al. (1968) and its predecessor (Roth & Hopkins,1953).

CAMCOG-R differs from CAMCOG in three ways:

(1) It includes two additional items to assess executivefunction in more detail; a verbal measure (ideationalfluency) and a non-verbal measure (visual reasoning).

(2) In addition to the six original items assessing remotememory (for the period of the 1930s and 40s), itcontains six alternative items (for the period of the1950s and 60s) which are intended for morerecently born cohorts.

(3) The tactile perception item (recognising two coinsplaced in the subject’s hand) has been omitted.This item proved problematic as new coins wereintroduced and normal elderly people often had dif-ficulty in recognising them. The omission of this itembrings the CAMCOG total down from the original107 to the new total of 105.

Scoring

CAMCOG provides subscale scores for hypotheticallydissociable functions, as well as a total score with amaximum of 105 points. Each item contributes between1 and 6 points to the relevant subscale and to the totalscore. For the animal fluency item, where elderly subjectsmay produce over 40 different animals, recoding is nec-essary, as specified in question 158.

Despite the addition of further tests of executive func-tion, the original CAMCOG scoring and total score has

82 Detailed description

not been changed, but a separate executive functionscore may be calculated (see p. 66).

Extended assessment of executive function

CAMCOG takes approximately 20 minutes to adminis-ter. Strict adherence by the interviewer to the printedinstructions for administration and coding is required toensure reliable scores.

Administration

Executive function is the term used to describe a varietyof high level cognitive processes including planning,organisation, abstraction, categorization, initiation, rea-soning, mental flexibility, sequencing and the allocationof attentional resources. Neuropsychological evidencesuggests that the frontal lobes play a key role in perfor-mance on tasks of executive function (e.g. Cummings,1993) and that performance on such tasks may be com-

promised relatively early in the course of dementia.Impaired executive function together with a relativepreservation of memory is indicative of dementia of thefrontal type (e.g. Gregory & Hodges, 1993).

Executive function is very difficult to assess briefly, bothbecause of the many different processes subsumedunder this rubric, and because most of the existing mea-sures (many still at an early stage of development) tendto be time-consuming. The original CAMCOG containstwo items which can be regarded as measures of execu-tive function. These are the Similarities questions whichassess abstraction, and the fluency item (animals) whichassesses initiation and categorisation. In view of theincreasingly prominent role of executive function mea-sures in cognitive assessment and dementia diagnosistwo further items have been added. The ideationalfluency item (‘How many different uses can you think of

Table 1 CAMCOG items and subscales

Subscale Maximum Score Sections Maximum Score

1 Orientation 10 Time 5Place 5

2 Language 30 Comprehension:motor response 4verbal response 3reading 2

Expression:naming 6fluency (animals) 6definitions 6repetition 1writing to dictation 2

3 Memory 27 Remote 6Recent 4New learning: incidental 12New learning: intertional 5

4 Attention and calculation 9 Serial sevens 5Counting backwards 2Calculation 2

5 Praxis 12 Copying 3Drawing 3Actions to command 6

6 Abstract thinking 8 Similarities 87 Perception 11 Tactile recognition* 2

Visual recognition 2Unusual views 6Recognise person 1

Total 107

* This item (recognising two coins) has been omitted from CAMCOG-R, changing the total from 107 to 105.

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for a bottle?’) is taken from a test battery developed byCrawford et al. (1995). It assesses initiation and mentalflexibility in the verbal domain. To assess executive func-tion in subjects who may have language problems, anon-verbal test of visual reasoning has been added. Ituses a format somewhat similar to Raven’s ProgressiveMatrices (Raven et al., 1976) and assesses sequencing,categorisation and abstraction.

The ideational fluency test has been validated in patientswith head injury, where it was found to be more sensitiveto impairment than other fluency tests (Crawford, 1995).Validation studies are currently underway in normalelderly and demented patients. The tests are included inadvance of published results, on the basis of their validityin other contexts and their brevity. They are inserted afterthe Similarities items (questions 197–200) and num-bered 200(a) and (b). Because of their provisional status,scores on these tests do not contribute to the totalCAMCOG score, which remains unchanged. A separateexecutive function score may be derived by adding thescores on these two items to the scores on similaritiesand animal fluency (see p. 66). For this purpose, bothideational fluency and animal fluency are recoded, bring-ing the maximum executive function score to 28.

CAMCOG Applications

CAMCOG has been used in many published investiga-tions both clinical (e.g. Hunter et al., 1989; Jobst et al.,1992a, b) and population-based (e.g. O’Connor et al.,1989; Brayne & Calloway, 1990; Clarke et al., 1991;

Cooper et al., 1992). It is currently being used in the UKin the Medical Research Council Multi-Centre Study ofCognitive Function and Ageing (MRC CFA Study) anddata will soon be available on over 3000 people aged65 years and older from a nationally representativesample, half of whom are being re-assessed annuallywith CAMCOG. This study will provide norms on an uns-elected elderly population as well as data on largenumbers of individuals with dementia.

To date, British norms are available only on a very elderlycohort in Cambridge City aged over 75 years (Huppertet al., 1995, 1996). Data from these studies are pre-sented in Tables 2 and 3.

CAMCOG Profile

For clinical work, it is often useful to have a visual profile ofan individual’s cognitive strengths and weaknesses. JeanHooper and Romola Bucks, two clinical psychologistsworking with older adults in Gloucestershire, have devel-oped the ‘Cognitive Profile’ (Hooper & Bucks, 1993)based on CAMCOG subscales, which is scored manually.

A CAMCOG profile can also be obtained using com-puter scoring and can be printed out from the CAMDEX-R disk. We are currently developing a computerisedmethod for examining an individual’s obtained versusexpected scores on the CAMCOG total and subscales,based on his/her sociodemographic characteristics.Health variables may also be included to examine theextent to which an individual’s cognitive impairment can

Table 2 Performance of an elderly population sample on CAMCOG subscales

Percent obtainingSubscale Maximum value Mean (SD) Median score maximum Range

Orientation 10 9.2 (1.0) 10 51 3–10Language 30 21.9 (2.6) 25 0 9–29Memory 27 20.7 (3.6) 21 0 4–26Attention 7 5.1 (1.9) 5 31 0–7Praxis 12 10.1 (2.0) 10 27 0–12Calculation 2 1.8 (0.4) 2 80 0–2Abstract thinking 8 5.2 (2.3) 5 20 0–8Perception 10* 7.8 (1.8) 8 16 1–10Total 106*

* For this community sample one item (recognising two people in the room) had to be omitted, reducing the number of itemsfrom 4 to 3, and the maximum score from 11 to 10. The total CAMCOG score was accordingly reduced from 107 to 106.Source: Huppert et al. (1995)

84 Detailed description

be explained by physical disorder or depression asopposed to dementia (see Jorm, 1994).

Camcog Scores and Sociodemographic variables

CAMCOG scores, like scores on any cognitive test withan adequate range, are markedly influenced by age, sex,education and social class. This can be seen in Table 4.For total CAMCOG score, all four variables exert a sig-nificant effect even when the other three variables havebeen controlled for. For CAMCOG subscales, the rela-tionship is more complex, with age exerting a significanteffect on almost all subscales while the other variablesshow selective effects. These findings make it clear thatsociodemographic variables must be taken into accountwhen judging whether an individual is impaired or notimpaired compared to the population average.

CAMCOG versus MMSE

CAMCOG examines a wider range of cognitive func-tions than the MMSE and includes items graded in diffi-culty. CAMCOG total score is more normally distributedthan MMSE scores (Fig. 1) and avoids ceiling effects.Figure 2 shows that elderly people who obtain maximumscores (29 or 30) on the MMSE are widely distributed interms of CAMCOG score.

Reliability

Total score on the CAMCOG was found to have excel-lent internal reliability (Cochran’s alpha 0.82, 0.89 in dif-ferent samples) and test–retest reliability (Pearsoncorrelation 0.86). The reliability of the individual sub-

Table 3 Mean scores of an elderly population sample on CAMCOG subscales

Age Group

77–79 80–84 85–89 90+ All AgesCAMCOG Subscales (n=135) (n=191) (n=64) (n=28)

Orientation 9.5 9.3 8.8 8.9 9.2Language 25.4 25.2 23.5 23.8 24.9Memory 21.7 21.0 18.9 18.6 20.7Attention 5.5 5.1 4.7 4.5 5.1Praxis 10.5 10.3 9.3 8.8 10.1Calculation 1.8 1.8 1.7 1.6 1.8Abstract thinking 5.6 5.2 4.4 4.6 5.1Perception 8.3 8.1 6.8 6.0 7.8

Source: Huppert et al., (1995)

Figure 1 (a) Distribution of CAMCOG scores(b) Distribution of MMSE scores

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scales, which corresponded to different cognitive abili-ties, and which may sample qualitatively differentprocesses, was also acceptable. (Pearson test-retestreliability 0.46–0.80). Reliability data are presented inmore detail in Huppert et al. (1996).

CAMCOG and Dementia

CAMCOG scores are very effective in differentiatingbetween demented and nondemented individuals.Huppert et al. (1996) report that in an elderly populationsample the CAMCOG total score, as well as eachsubscale score, differed significantly between non-demented individuals and those with the diagnosis ofmild dementia or minimal dementia (Table 5). As well asdifferentiating between groups, CAMCOG also differen-tiates successfully between individuals. CAMCOG totalscores showed high levels of sensitivity and specificity indifferentiating between non-demented individuals andthose with a diagnosis of mild dementia. The cut-pointwhich produced the highest levels of both sensitivity andspecificity was 80/81, with values of 93% and 87%,

respectively (Table 6). CAMCOG score also predictsdementia diagnosis. For each 1 point decrease in score,there is a 20% increase in the probability of dementiadiagnosis.

These findings are described in more detail in Huppert etal. (1996).

Figure 2 CAMCOG score for high MMSE scorers (29 or 30)

Table 4 Sociodemographic variables and CAMCOG performance

CAMCOG score

No. Female (%) Mean (SD) Median Range

SexMale 137 87.4 (9.5) 90 52–102Female 281 67 83.7 (11.5) 86 31–102

Age (years)77–79 135 64 88.3 (9.1) 89 48–10280–84 191 68 86.1 (9.8) 88 55–10285–89 64 67 78.1 (13.3) 81 31–10090+ 28 82 76.6 (10.7) 80 51–89

Education* (age at leaving school)12/13 52 71 80.0 (12.8) 83 31–9814 242 64 84.3 (10.2) 86 48–10215 52 73 88.0 (10.9) 90 51–10216 44 66 87.5 (12.3) 92.5 52–10017+ 26 88 90.4 (7.1) 91 67–100

Social class*Professional/managerial 82 68 86.1 (10.9) 88 51–102Skilled non-manual 74 73 88.2 (10.3) 90 48–102Skilled manual 148 62 85.7 (10.1) 87.5 51–100Semi-skilled/unskilled manual 103 69 81.4 (12.1) 85 31–102

* It was not possible to establish education for 2 respondents, and social class for 1 respondent.Source: Huppert et al. (1995)

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Table 5 Means (and SDs) on Cambridge Cognitive Examination (CAMCOG) and its Subscales as aFunction of Dementia Severity

Non-demented Minimal dementia Mild dementia

Subscale Mean (SD) Mean (SD) Mean (SD)

Orientation** 9.73 (0.57) 9.03 (0.96) 7.19 (1.83)

Language** 26.13 (2.27) 24.01 (2.20) 22.16 (3.75)Comprehension** 8.66 (0.63) 8.33 (0.82) 7.67 (1.34)Expression* 17.44 (2.00) 15.68 (1.83) 14.58 (2.83)

Memory** 22.18 (2.67) 18.41 (4.20) 14.74 (4.55)Remote Memory** 4.75 (1.21) 3.97 (1.44) 2.94 (1.47)Recent Memory** 3.82 (0.46) 3.37 (0.85) 2.23 (1.23)Learning** 13.56 (1.88) 11.09 (3.04) 9.30 (3.55)

Attention/Calculation* 6.91 (2.14) 5.16 (2.38) 4.32 (2.37)

Praxis** 1.57 (1.64) 9.40 (1.90) 8.10 (2.11)

Abstract Thinking** 5.78 (2.13) 4.64 (2.41) 2.58 (2.15)

Perception* 7.87 (1.80) 6.89 (1.88) 6.20 (1.53)

CAMCOG** 89.69 (8.49) 77.95 (9.72) 65.46 (1.69)

Note: Because of missing data, n = 291–322 for non-demented, 64–71 for minimal dementia and 41–53 for mild dementia.** All group means differ, P <0.01.* Non-demented group differs from minimal and mild groups, P < 0.01.Source: Huppert et al. (1996)

Table 6 Sensitivity and Specificity of CambridgeCognitive Examination (CAMCOG) at Various Cutpoints

Cutpoint Sensitivity Specificity

65 / 66 51 9966 / 67 51 9867 / 68 56 9868 / 69 61 9869 / 70 66 9870 / 71 66 9771 / 72 71 9772 / 73 76 9673 / 74 83 9574 / 75 85 9475 / 76 85 9276 / 77 85 9277 / 78 85 9178 / 79 85 9079 / 80 90 8880 / 81 93 8781 / 82 93 8682 / 83 93 8483 / 84 98 81

Source: Huppert et al. (1996).