Normative study of the category fluency test (CFT) from nationwide data on community-dwelling elderly in Korea

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Abstract

Objectives: We determined the influence of demographic characteristics on the categorical verbal fluency and to provided its’ normative data for the community-dwelling elderly with diverse educational attainment. Methods: We administered the CFT using the animal category to 3025 (1420 men and 1605 women) non-demented community-dwelling Koreans aged 60–96 years who had educational levels ranging from 0 to 22 years. Results: Age and education were associated significantly with performance of CFT, with education showing the stronger association. Education accounted for 14.0% of CFT score variance and age accounted for 3.2%. However, gender did not influence performance of the test. We present normative data for CFT stratified by age (60–64, 65–69, 70–74, 75–79, 80–84, and ≥85 years) and education (0, 1–3, 4–6, 7–9, 10–12, and ≥13 years). Conclusions: The CFT norms should provide clinically useful data for evaluating elderly people and help improve the interpretation of verbal fluency tasks and allow for greater diagnostic accuracy for cognitive disorders such as Alzheimer's disease (AD).

Introduction

Assessment of verbal fluency has long been used for evaluating patient executive function, semantic memory and language (Benton, 1968, Lezak, 1995). Patient verbal fluency is typically tested in letter and category domains that are based on phonemic and semantic fluency, respectively. Clinicians most commonly assess letter fluency via various forms of the Controlled Oral Word Association Test (COWAT), which requires participants to produce words beginning with a certain letter of the alphabet (Ruff et al., 1996). In a category fluency assessment, participants are asked to name examples belonging in a particular category in 60 s trials. Clinicians most commonly employ the category “animals” (Rosen, 1980). This requires the participant to name as many animals as possible. Research has shown both these verbal fluency measures are sensitive to brain damage (Butters et al., 1987, Janowsky et al., 1989, Stuss et al., 1998).

Category fluency and letter fluency differentially involve specific frontal and temporal lobe sites, and semantic fluency may be more sensitive to such damage than letter fluency is (Henry et al., 2004). Researchers have also demonstrated that differential performances on letter versus category fluencies have diagnostic utility in aging-related disorders, such as AD (Rosen, 1980, Monsch et al., 1992, Barr and Brandt, 1996). AD particularly reduces category fluency, whereas letter fluency remains relatively intact (Monsch et al., 1992). These observations are consistent with findings showing temporal systems mediate category fluency performance (Pihlajamaki et al., 2000) and frontal systems underlie letter fluency performance (Abrahams et al., 2003). Therefore, the CFT may be a useful screening tool for mild AD (Caramelli et al., 2007). Even though this test can detect dementia, clinicians should consider demographic influences when using the CFT to screen or evaluate patients, as many studies have shown age, education, and even gender influence this test (Rosselli et al., 1990, Kempler et al., 1998, Ratcliff et al., 1998, Carnero et al., 1999, Ostrosky-Solis et al., 1999, Acevedo et al., 2000, Brucki and Rocha, 2004, Lee et al., 2004).

Korea's population is rapidly aging, and the elderly have very diverse literacy and formal education levels. It is important to determine demographic profiles’ influences on categorical verbal fluency. Furthermore, correct evaluations of the elderly who have cognitive impairments and/or dementia illnesses require normative data stratified by age, education, and gender. We aimed to investigate the effects of age, education, and gender on categorical verbal fluency and to provide normative data for the educationally diverse elderly population in Korea.

Section snippets

Study population and measurements

All participants were community-dwelling persons, aged 60 years or older, who participated in four community-based cohort studies: the Korean Longitudinal Study on Health and Aging (KLoSHA) (Park et al., 2007), the Ansan Geriatric Study (AGE) (Jo et al., 2007), the Gwangju Dementia and Mild Cognitive Impairment Study (GDEMCIS) (Lee et al., 2009), and the Nationwide Survey on Dementia Epidemiology of Korea (NaSDEK) (Kim et al., 2011). Informed consent was obtained from each participant,

Demographic characteristics

We constructed the normative data using information on 3025 participants (1420 men and 1605 women); Table 1 shows their demographic characteristics. The mean educational level of the males, who were 47% of total participants, was significantly higher than that of the females (t = 27.60, p < 0.001). Mean participant age was 71.7 (SD = 6.7) and ranged from 60 to 96 years. The mean years spent in full-time education was 7.4 (SD = 5.2), with a range of 0–22 years.

Effects of age, education, and gender on CFT score

Stepwise multiple regression analysis

Discussion

The present study examined the influence of age, gender, and education on CFT performance and derived normative information from an educationally diverse elderly population, to allow clinicians and researchers to better interpret CFT results.

In our population, we found age and education associated with CFT performance but gender did not, which is consistent with our previous study on 618 healthy, elderly Koreans (Lee et al., 2004). Most previous studies have found no gender effect on CFT

Conclusions

This study shows education and age, but not gender, influence category fluency in the elderly. Moreover, it shows education is the most influential demographic factor. Finally, this study provides age- and education-specific normative CFT data for Korean elderly.

Conflicts of interest

None.

Acknowledgment

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST). (Grant No. 2010-0029382).

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