Original Article
Mini-Mental Status Examination: A short form of MMSE was as accurate as the original MMSE in predicting dementia

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Abstract

Objectives

This study assesses the properties of the Mini-Mental State Examination (MMSE) with the purpose of improving the efficiencies of the methods of screening for cognitive impairment and dementia. A specific purpose was to determine whether an abbreviated version would be as accurate as the original MMSE in predicting dementia.

Study Design and Setting

A population-based post hoc examination of the performance characteristics of the MMSE for detecting dementia in an existing data set of 243 elderly persons.

Results

Sensitivity, specificity, and predictive values were computed for the original MMSE as well as new MMSE scale models derived from a Rasch model item analysis. The optimal threshold for the original MMSE screen yielded sensitivity and specificity estimates of 72.5% and 91.3%, respectively. The use of a subscale resulted in a slightly lower sensitivity (71.0%), specificity (88.4%), and positive predictive value (71.0%) but equal area under the receiver operating characteristic curve. Cross-validation on follow-up data confirmed the results.

Conclusion

A short, valid MMSE, which is as sensitive and specific as the original MMSE for the screening of cognitive impairments and dementia is attractive for research and clinical practice, particularly if predictive power can be enhanced by combining the short MMSE with neuropsychological tests or informant reports.

Introduction

As the general population of most countries ages, there is an increasing need for brief, but sensitive and specific screening instruments for dementia and cognitive impairment. Accurate diagnosis of cases early in the course of dementia is desirable to identify those with dementia for early interventions, treatment, and planning of healthcare. Furthermore, these measures may be used for epidemiological studies of incidence and prevalence rates.

Among the brief cognitive tests that have been proposed as a screening measure for dementia and cognitive impairment in either research settings or particular clinical situations, the Mini-Mental State Examination (MMSE) [1] is one of the most frequently used and extensively studied with regard to precision and accuracy [2], [3], [4], [5], [6], [7], [8], [9]. A score of 23 or less has generally been accepted as indicating the presence of cognitive impairment. Most studies that have used this criterion score to identify cases with dementia, report moderate to high levels of sensitivity and specificity of the MMSE in clinical series [1], [4], [10], [11]. However, recently it has been pointed out that the sensitivity of the MMSE is lower when patients in the early stages of dementia are examined [4], [11], [12], [13]. In the last several years, epidemiological research has further shown that some MMSE items are biased with respect to age, education, and ethnicity [14], [15], [16], [17], [18]. This suggests that different subjects with similar levels of impairment are assigned different diagnoses.

Fundamentally, two approaches may be used to increase the performance of the MMSE as a screening test for dementia. The first approach is to adjust the cut-point for the MMSE score. The easy method of this first approach, raising the cut-point, increases the sensitivity but sacrifices specificity. Another method of this approach is to use population-based norms, taking age and education into account. Some researchers have proposed more specific recommendations of how to make age- and education-adjusted MMSE cut-points [8], [17], [18]. However, the correction for age and education of the raw score of the MMSE cannot be generalized across space and time and has also been shown to cause reduction in the sensitivity of the MMSE [19], [20], [21]. The second approach to increase the performance of the MMSE is by improving the structure of the scale and the content of specific items. For instance, those working with this approach have attempted to identify the most efficient items for detecting cognitive impairment and dementia [13], [22], [23], [24] or have added items [25]. In the present study, we have addressed this second approach by exploring constructs of cognitive dimensions and diagnostic cut-points on the basis of empirically derived selections of items.

In the first stage of the study (reported in the companion paper [28]), an item analysis by conventional and mixed Rasch models [26], [27] identified two separate constructs of cognitive dimensions indicating that there are two MMSE measurements, which cannot be summed up or replaced by each other. In addition, the findings indicated that the study sample consisted of a mixture of at least two different latent classes of elderly people categorized on the assumptions of qualitatively different strategies in their performance of the MMSE [28]. In this paper, the criterion-related validity of different scoring systems of the MMSE is studied. A secondary purpose has been to determine whether a unidimensional MMSE subscale will be as sensitive and specific as the original MMSE in predicting dementia. Thirdly, we have determined the extent to which the original polytomous scoring of five MMSE items provides more essential information in relation to dementia compared to a dichotomous scoring.

To pursue these aims, we have used data on MMSE, cognitive function, and dementia from a community-based study of 1,782 elderly residents in a district of Copenhagen (the Brønshøj–Husum Study). Study design and number of subjects included in the study are presented in Fig. 1 of the companion paper [28]. The description of the characteristics of the basic study population, the subsample of 243 initial respondents, and the follow-up sample presented (Fig. 1 and Table 1) are the same for this article as well as the companion paper. In the companion paper, the percentages of correct responses for individual MMSE items in the same three study samples are given in Table 2 [28].

Section snippets

Screening

In the first stage of the study, MMSE was administered by one of three home nurses in a quiet location of the subject's home. At follow-up, the MMSE was administered by the research psychologist as a preliminary to the clinical neuropsychological examination, which took place in the participant's home. At baseline examination, the psychologist was blinded to the MMSE results. Measures and coding of MMSE responses are the same as those of the companion paper [28].

The criteria of diagnosis

The neuropsychological

Subject characteristics

The demographic characteristics, screening results, and clinical diagnosis for the samples at initial entry and follow-up are given in Table 1 of the companion paper [28]. The study samples had an age range from 75 to 85 years. Approximately 65% of the population had seven or less years of school education, approximately 13% of the population had qualified for tertiary education. The relative increase in the prevalence of dementia among the subsample of the 243 participants (28.4%) and in the

Discussion

Most studies that have been undertaken so far to explore factor structure and cognitive dimensions of the MMSE have yielded conceptually conflicting results [22], [23], [37], [38], [39], [40], [41] without implications that may be of direct value to the practitioner or the researcher. To our knowledge, this is the first study intended to test the criterion-related validity of empirically derived cognitive dimensions of the MMSE in comparison with the original MMSE.

The combined sensitivity of

Acknowledgments

This study was supported by grants from the Danish Ministry of Social Affairs, The Copenhagen Care and Health Administration, and VELUX FONDEN of 1981.

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