Cognitive testing of elderly Chinese people in Singapore: influence of education and age on normative scores

Age and Ageing, Nov, 1997 by Suresh Sahadevan, Noellyn J.L. Tan, Tahchew Tan, Shirley Tan

Introduction

Dementia affects 2-4% of elderly people (defined as being 65 years of age or older) in Singapore [1, 2], where the size of the elderly population is expected to triple over the next three decades, reaching 20% by 2030 [3]. By then the numbers with cognitive impairment are estimated to reach 20 000. Furthermore, epidemiological studies of the local prevalence rates [1, 2] may have only picked up cases of established dementia; if those in the earlier stages are also included, numbers will be far larger.

The diagnosis of dementia has been made easier by employing well-defined clinical criteria [4-6] and by psychometric testing. Cultural, educational and ethnic factors must however be considered when drawing conclusions from psychological tests obtained in populations differing from the ones in which they were validated. This prompted our study. We have already described the methodology and presented the overall mean scores of the neuropsychological assessment battery [7]: here, we focus upon the influence of the subjects' age and educational attainments on their test performances and describe the rationale of the methods employed to derive our table of normative values.

Method

Design

The main aim of this community study was to identify cognitively intact elderly subjects based upon predefined criteria and to apply selected psychological as well as cognitive screening tests to them. The master list of subjects was obtained from the membership records of seven randomly chosen senior citizens' clubs as well as the retirees' club; these clubs are affiliates of a statutory body and organize recreational and community activities for the well elderly of Singapore.

Singapore is a cosmopolitan country and its 1990 census shows the ethnic composition to be Chinese (78%), Malay (14%) and Indian (7%) [8]. Amongst those who were 50 years of age and above in 1990, 72.3% had no formal or an incomplete primary education. Women made up 49.6% of the population. To avoid the confounding influence of different cultures, only Chinese subjects of the major dialect groups (Mandarin, Hokkien, Teochew) were enrolled into the study. The subjects were stratified according to gender, age (60-64 years, 65-74 years and 75-84 years) and educational exposure (0 years of education, 1-6 years of education and [is greater than] 6 years of education).

From the master list we intended to study 180 elderly subjects from all the age-, education- and genderspecified categories mentioned above. A telephone interview was first conducted with the subjects, whereby their response to a 10-question elderly cognitive assessment questionnaire--a locally validated cognitive screening instrument [9]--was elicited, as well as information on medication, functional status and alcohol consumption. A separate telephone interview with the subject's principal care-giver was also conducted to pick up features of dementia or depression. A home visit, with permission, was then made by the research psychologist to administer the neuropsychological assessment battery.

All tests and procedures were approved b) the hospital's ethics committee and were conducted with the informed consent of both subjects and principal care-givers.

Definitions

To identify cognitive normality, we used the following criteria: (i) scoring [is greater than] 7 on the elderly cognitive assessment questionnaire (earlier validation. work [9] had shown that locally a score of 5 and below identified dementia); (ii) not having any of the features indicative of dementia as set out by the American Psychiatric Association's Diagnostic and Statistic41 Manual IV criteria [4]; (iii) not having a history or current features of depression or other psychiatric conditions or stroke; (iv) not having a regular intake of sedatives or a history of heavy alcohol intake (defined as more than one bottle of spirits at each drinking session and/or a frequency of more than one drinking session per week); (v) not being housebound or dependent for any of the basic activities of daily living (the aim being to exclude those with serious physical disability).

We wished to ensure that those described as `normal' were reasonably so, while at the same time avoiding the formation of a `super-normal' group (whose performance scores could not be usefully extrapolated to `average' patients).

Neuropsychological assessment battery

The two main groups of tests in the neuropsychological assessment were brief cognitive screening tests and the more detailed psychological tests, which probed different aspects of cognition.

Two cognitive screening instruments were analysed. The Abbreviated Mental Test [10] assesses memory, concentration and orientation. The Chinese Mini-Mental Status [11] also assesses these functions, along with language, calculations and visuo-spatial abilities.

The following eight psychological tests were selected because of their brevity (the entire battery was completed within 45 min for each subject) and ease of administration, as well as their ability to assess the characteristic impairments accompanying dementia in the domains of memory, language, visuo-spatial abilities and executive functioning: