Three sides of the same coin: measuring global cognitive impairment with the MMSE, ADAS-cog and CAMCOG.
OBJECTIVE
The total scores of the ADAS-cog, MMSE and CAMCOG, comprising various cognitive tasks, are widely used to measure a dimension of global cognitive impairment. It is unknown, however, whether this dimension is common to these instruments. This hampers comparisons when either of these instruments is used. The extent to which these instruments share a common dimension of global cognitive impairment and how their scores relate was examined.


METHODS
Rasch analysis of CAMCOG and MMSE data of participants from a population based study and two memory clinics pooled with ADAS-cog and MMSE data of participants from three RCTs (overall N = 1566) to estimate a common dimension of global cognitive impairment and to examine the goodness of fit of the individual items to this dimension.


RESULTS
Using the estimated common dimension of global cognitive impairment, the total scores of the instruments could be related, e.g. a mean level of global cognitive impairment corresponded to a predicted score of 11.4 (ADAS-cog), 72.6 (CAMCOG) and 22.2 (MMSE). When revised according to The Rasch validity analyses, every individual item could be fitted to the dimension.


CONCLUSIONS
The MMSE, ADAS-cog and CAMCOG reflect a valid common dimension of global cognitive impairment, which enables comparisons of RCTs that use the ADAS-cog and observational studies that use the CAMCOG and MMSE.
Wouters
Hans
H
Department of Clinical Epidemiology, Biostatistics and Bioinformatics, Academic Medical Center, University of Amsterdam, The Netherlands. J.Wouters@amc.uva.nl
van Gool
Willem A
WA
Schmand
Ben
B
Zwinderman
Aeilko H
AH
Lindeboom
Robert
R
D000368:Aged; D000369:Aged, 80 and over; D003072:Cognition Disorders / Q000175:diagnosis* / Q000523:psychology; D005260:Female; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests / Q000592:standards*; D011569:Psychiatric Status Rating Scales / Q000592:standards*