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. Author manuscript; available in PMC: 2011 May 3.
Published in final edited form as: Appl Neuropsychol. 2008;15(2):97–106. doi: 10.1080/09084280802083863

FAS and CFL Forms of Verbal Fluency Differ in Difficulty: A Meta-analytic Study

Danielle Barry 1, Marsha E Bates 2, Erich Labouvie 2
PMCID: PMC3085831  NIHMSID: NIHMS249551  PMID: 18568601

Abstract

The Controlled Oral Word Association (COWA) Test is a brief and sensitive measure of executive cognitive dysfunction. There are two commonly used forms of the test, one using the letters F, A, and S, and the other using C, F, and L. This study examines the relative difficulty of the two forms using a meta-analytic approach that includes multiple samples of normal individuals. The effects of age, education, gender composition, exclusion criteria, and age of study are also examined. Results indicate that the CFL form of the test is more difficult and that age, education, and the use of strict exclusion criteria influence performance. Performance is more variable for the FAS form, and age and age of study influence performance variability.

Keywords: Verbal Fluency, Controlled Oral Word Association Test, COWA, FAS, CFL

Introduction

An oral Verbal Fluency Test was first developed by Arthur Benton over 40 years ago (Mitrushina, Boone, & D'Elia, 1998). It was included in the Multilingual Aphasia Examination (Benton & Hamsher, 1976) in a slightly different form and with a new name, the Controlled Oral Word Association (COWA) Test. This test, also known as the phonemic or letter fluency test, requires test takers to name as many words beginning with a single letter as they can in one minute. Standard administration provides three letters. The most commonly used form of the test today uses the letters F, A, and S (Spreen & Strauss, 1998), but the form included in the Multilingual Aphasia Examination (Benton & Hamsher, 1976) uses the letters C, F, and L or P, R, and W. Although the name COWA is most accurately applied to the CFL/PRW form of the test, it has been widely adopted to describe the FAS form as well. Other versions of the letter fluency test that use different letters or different numbers of letters are included in a variety of test batteries (Spreen & Strauss, 1998). For example, the Test of Verbal Conceptualization and Fluency (TVCF; Reynolds & Horton, 2006) includes a verbal fluency test employing the letters P, D, S, and T, and the Delis-Kaplan Executive Function Scale (D-KEFS; Delis, Kaplan, & Kramer, 2001) includes the FAS form and a version using B, H, and R. Although it was developed as a test of verbal ability, the COWA is also considered a test of executive functions, including cognitive organization, initiation, maintenance of effort, and the ability to conduct a non-routine search for words based on a specific first letter, rather than lexical definition (Andrewes, 2001; Devinsky & D'Esposito, 2004; Walsh & Darby, 1999). This interpretation is consistent with research showing poor performance in individuals with frontal lobe lesions (Ruff, Allen, Farrow, Niemann, & Wylie, 1994; Walsh & Darby, 1999) and sensitivity to cognitive dysfunction in disorders that affect executive functions (Henry & Beatty, 2006).

There is some evidence that different forms of the COWA have different levels of difficulty. Borkowski, Benton, and Spreen (1967) classified the letters C, F, P, A, and S as easy letters and the letters L and R as difficult letters based on the English vocabulary size for each letter. The FAS test thus includes only easy letters, whereas the CFL/PRW norms are based on fluency in response to two easy and one difficult letter (Bolla et al., 1990; Lacy et al., 1996; Ruff, Light, Parker, & Levin, 1996). Although comparison of norms for the FAS and CFL forms of the COWA suggest some differences in difficulty, these differences are difficult to interpret due to the use of different samples for each form (see Spreen & Strauss, 1998, for summary). Lacy et al. (1996) studied the equivalence of the two forms in a sample of 287 patients with various neuropsychological complaints. They administered the letters A, C, F, L, and S to each patient in various orders and then compared performance on CFL and FAS groupings. The two forms correlated highly in all patient groups, suggesting that interpretation of FAS using CFL norms would be accurate, at least in clinical samples (Lacy et al., 1996).

In addition to the form of test used, effects of demographic variables are important to consider when interpreting COWA results. Age effects have failed to emerge in many studies (Axelrod & Henry, 1992; Bolla et al., 1990; Ruff et al., 1996; Selnes et al., 1991), although some studies have shown modest age effects, with higher age predicting poorer performance (Libon et al., 1994). Higher education has been associated with better COWA performance in several studies (Ruff et al., 1996; Selnes et al., 1991; Tombaugh, Kozak, & Rees, 1999). Some studies find superior performance on the COWA in women compared to men (Bolla et al., 1990; Ruff et al., 1996), although other studies find no difference between men and women (Boone, 1999; Saykin et al., 1995; Tombaugh et al., 1999).

This study uses multiple regression analysis to examine the influence of form of administration (FAS or CFL) on COWA performance in a large sample comprising multiple published and unpublished studies of normal participants. It also examines the influence of age, education, and gender on mean performance. Influences on the variability of performance were also examined by analyzing the effect of independent variables on the standard deviation of the mean. The meta-analytic methodology employed allows for the examination of two other factors that could influence the applicability of normative samples: the strictness of the exclusion criteria, and the recency of data collection.

Method

Data Collection

Data were collected from published journal articles, normative studies, and unpublished dissertations reporting data obtained from normal, English-speaking participants. Studies were identified through searches of three computerized databases, PsychInfo, Medline, and Web of Science, using the terms verbal fluency test, controlled oral word association, COWA, and word fluency as keywords. A manual search of issues of Neuropsychology, The Clinical Neuropsychologist, the Journal of Clinical and Experimental Neuropsychology, Archives of Clinical Neuropsychology, and the Journal of the International Neuropsychological Society between 1997 and March 2006 was also conducted. Additional studies were identified from the references in studies obtained by the first two methods. Once identified, publications examining normal participants and reporting mean scores for the tests and at least one of three demographic variables (age, education, or gender composition) were included. Studies that used non-standard test administration procedures or that failed to report the form of COWA used were excluded. Only studies conducted in the United States or Canada were used, because differences in educational systems in other English-speaking countries would interfere with analysis of education effects.

Procedure

The following data were entered into an Excel spreadsheet for each study: mean test score, standard deviation of the mean, age, education, gender composition, year of study, exclusion criteria, and form of test (FAS, CFL) used. Test form and exclusion criteria were dummy coded for inclusion in the regression analysis. Studies using the FAS form of the COWA were coded 1, and those using the CFL form were coded 2. Studies that excluded participants based on at least three characteristics (history of neurological illness, history of significant head injury, history of psychiatric illness, history of significant medical illness, current substance use disorder), were coded 1, and those that did not employ at least three exclusion criteria were coded 0. The sample included 134 studies. Table 1 shows the demographic characteristics of the studies, and Table 2 shows characteristics of the sample included.

Table 1.

Demographic Characteristics of the Sample

N 134
Mean Score (SD) 40.18 (6.02)
Mean Standard Deviation (SD) 11.23 (2.12)
Mean Age (SD) 53.63 (19.65)
Mean Education (SD) 13.94 (2.01)
Average % Male Participants (SD) 50% (31)
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Table 2.

Characteristics of Studies

Mean Age of Study 8.99 (4.36)
Number Employing Strict Exclusion Criteria 85
Number Using FAS Form 112
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Data Analysis

Mplus statistical software (Muthén & Muthén, 1998) was used for data analysis. A full information maximum likelihood (FIML) method was used to produce unbiased parameter estimates assuming that data are missing at random (Allison, 2001; Muthén & Muthén). Multiple regression analyses yielded regression equations for the sample means and standard deviations of each test. Following the initial analyses, regression weights of non-significant variables were set to zero, and the analyses rerun, in order to obtain model fit indices. Variables that approached but did not reach significance were not set to zero. Most independent variables were normally distributed. Education was negatively skewed, indicating a higher proportion of scores at the higher end of the distribution. Square root, log, and inverse transformations were conducted on the education variable, but these transformations did not alter the results of the analyses, so the original analyses with untransformed variables were retained in order to avoid difficulty interpreting the effects of substantive differences in independent variables. Effect sizes for each independent variable were obtained as the unique variance accounted for by that variable.

Results

The regression equation for the mean fit the data well when non-significant variables were set to zero (χ2 = 0.831, df = 2, p= 0.6582, RMSEA = 0.00, 90% CI = 0.00 – 0.13, SRMR = 0.01, CFI = 1.00, TLI = 1.00). Gender and year of study were not significant in the preliminary analysis and were set to zero for the purpose of obtaining fit indices. Age and education were significantly associated with mean performance on the Verbal Fluency Test. Older age predicted worse performance, higher education predicted better performance, and the effect sizes for both variables were large. Exclusion criteria also had a significant effect on mean performance. More words were produced in studies with stricter exclusion criteria, with a medium effect size. Test form was also a significant predictor of mean performance, with worse mean performance in studies using the CFL form, but the effect size was small. The mean score for the FAS form of the test was 40.48 (6.08), and the mean score for the CFL form was 38.66 (5.55). The independent variables accounted for 47% of the variance in mean scores.

The regression equation for the standard deviation of the mean also fit the data well when non-significant variables were set to zero (χ2 = 2.489, df = 3, p = 0.4762, RMSEA = 0.00, 90% CI = 0.00 – 0.14, SRMR = 0.02, CFI = 1.00, TLI = 1.00). Age was associated with standard deviation; there was greater variability in older samples. Age of study also predicted variability of performance, with less variability in older studies. Form was a significant predictor of standard deviation as well, suggesting greater variability in samples employing the FAS form of the Verbal Fluency Test. The effect sizes for age of study and form were large. The independent variables accounted for 15% of the variance in the standard deviation of COWA performance.

Table 3 shows the unstandardized beta weights for each variable retained in the second analysis. Table 4 shows the effect sizes represented as percent of variance accounted for by each variable.

Table 3.

Estimates for Demographic and Study Variables (Unstandardized Beta Weights)

Variable Mean Standard Deviation
Age −0.093** 0.028**
Education 1.534** 0
% Male 0 0
Exclusion Criteria 3.274** 0
Age of Study 0 −1.242**
Form of Test −2.401* −0.113**
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*

p<0.05

**

p<0.01

Table 4.

Variance in Means Accounted for by Independent Variables

Variable Mean Standard Deviation
R2 0.468 0.151
% R2 accounted for by:
Age 29.5 45.6
Education 54.3
% Male
Exclusion Criteria 13.5
Age of Study 27.8
Form of Test 2.7 26.5
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Magnitude of effect sizes: Small (1-2% of variance), Medium (5-10%), Large (15% or more).

Conclusions

The results of this study suggest that the CFL form of the COWA Test is more difficult than the FAS form and that there is greater variability in performance on the FAS form among normal individuals. Because the range of normal scores is narrower for CFL, interpretation of results from the two forms could be different for individuals whose scores lie at the extremes of the distribution where the effect of differences in standard deviations may be amplified. These results are inconsistent with findings from the study by Lacy et al. (1996) showing comparable performance on the two forms in clinical samples. One implication of these results is that performance on one form of the test cannot be accurately interpreted using norms based on the other form. Similarly, comparisons of raw scores on the two forms of the test, such as might be used in a pre- and post-intervention evaluation of cognitive ability, should be made cautiously, if at all.

Although previous studies have been inconsistent in their support of age as a variable influencing COWA performance, this study indicates that older adults will perform more poorly than younger adults and that their performance will be more variable. Verbal ability is generally considered a crystallized ability, one that does not decline with age or in response to subtle brain dysfunction, but verbal fluency, particularly phonemic fluency, requires executive ability, specifically the ability to initiate and maintain effort and organize information for retrieval, abilities that are sensitive to subtle cerebral dysfunction and aging (Bryan & Luszez, 2000; Burke & Barnes, 2006; Henry & Beatty, 2006; Mittenberg, Seidenberg, O'Leary, & DiGiulio, 1989; Plumet, Gil, & Gaonac'h, 2005). Education was a potent predictor of performance, consistent with prior research. Higher education predicted better performance. Previous research on the effect of gender on Verbal Fluency performance has been inconsistent. This study indicates that gender does not influence verbal fluency.

Overall, these results support the importance of using norms stratified by age and education, but not gender, when interpreting COWA performance and suggest caution in using the two forms of the test interchangeably.

Acknowledgments

This study was supported by the National Institute of Alcohol Abuse and Alcoholism Grants R01 AA11594, and K02 AA00325.

Appendix A

Studies included in the analysis.

Study N Mean
Score		 SD Mean
Age		 Mean
Education		 % Male Strict
Exclusion
Criteria		 Form
Axelrod & Henry (1992) 20 41.1 9.9 55.3 15.4 50 Yes FAS
20 39.6 10.7 65.2 14.4 50 Yes FAS
20 36.0 9.3 74.3 14.5 50 Yes FAS
20 37.8 14.0 83.4 14.5 40 Yes FAS
Basso et al. (2002) 31 44.0 9.16 34.09 14.91 9 Yes FAS
Basso et al. (1999) 82 47.68 10.82 31.9 14.56 100 Yes FAS
Beatty et al. (1989) 13 39.5 11.6 65.4 14.4 Yes FAS
15 38.4 8.2 63.9 11.0 Yes FAS
Berry et al. (1993) 21 41.6 10.7 33.2 14.1 95 Yes FAS
Bolla et al. (1990) 32 38 12 61 13 100 Yes FAS
25 43 12 63 14 100 Yes FAS
23 47 9 65 17 100 Yes FAS
33 42 9 61 13 0 Yes FAS
39 46 12 65 15 0 Yes FAS
47 49 12 69 16 0 Yes FAS
Bolla et al. (1999) 21 36.3 10.0 33.9 12.6 81 Yes FAS
Bondi et al. (2003) 43 39.05 10.29 66.72 14.67 56 No FAS
36 39.31 12.01 79.17 14.53 50 No FAS
Boone et al. (1990) 25 43.56 6.51 54.5 14.68 Yes FAS
21 42.33 14.21 64.5 13.81 Yes FAS
15 36.0 8.93 74.5 14.53 Yes FAS
Boone et al. (1995) 110 40.45 11.12 63.1 14.8 47 Yes FAS
Caccappolo-Van Vliet et al. (2003) 155 39.0 67.9 15.1 40 No CFL
Carone et al. (2005) 37 42.2 10.2 42.3 15.0 *** Yes CFL
Cerhan et al. (2002) 221 34.01 11.31 76.1 13.7 41 Yes CFL
Cerhan et al. (1998) 622 34.8 12.6 47 100 No FAS
1598 33.2 12.5 52 100 No FAS
1542 32.6 12.7 57 100 No FAS
1495 32.0 12.6 62 100 No FAS
846 31.6 13.0 67 100 No FAS
897 35.8 12.0 47 0 No FAS
2182 34.6 12.4 52 0 No FAS
2010 33.6 12.1 57 0 No FAS
1724 32.7 12.1 62 0 No FAS
864 31.8 12.6 67 0 No FAS
Clark et al. (1997) 92 41.4 10.3 35.5 13.9 29 No FAS
Clark et al. (2001) 30 48.7 13.8 37.6 15.6 53 No CFL
Comilang (2003) 124 42.26 9.1 19.9 26 Yes CFL
Connor et al. (2000) 15 45.5 11.8 24.3 100 Yes FAS
Crossley et al. (1997) 139 24.0 12.4 69.6 8.2 No FAS
343 25.8 11.5 79.0 9.1 No FAS
146 24.0 10.8 87.8 8.8 No FAS
Crowell et al. (2002) 80 33.56 10.7 37.95 12.98 100 No FAS
DeLuca et al. (1998) 20 42.5 2.0 42.2 15.5 No CFL
Demakis (1999) 21 37.8 11.1 22.5 13.6 33 No CFL
Dinn & Harris (2000) 10 41.6 9.0 28.9 13.9 100 Yes FAS
Dursun et al. (2002) 47 54 16 39 16.09 0 No FAS
28 57 15 27 14 100 No FAS
Elmudesi (1995) 9 28.22 6.76 36.89 14.0 100 No CFL
Feinstein et al. (1998) 11 44.1 12.0 25.3 Yes FAS
Friedman et al. (1995) 24 44.29 12.5 35.8 Yes FAS
Friend et al. (1999) 42 45.31 12.96 45.83 14.38 17 Yes CFL
Garrett (2004) 25 40.7 15.2 76.5 12.4 44 Yes FAS
Goldstein et al. (2001) 14 32.3 7.7 65.3 13.4 64 Yes FAS
Gopal (1996) 10 47.7 9.74 40.3 14.3 90 Yes FAS
Gourovitch et al. (1996) 24 42.36 33.04 14.04 22 Yes FAS
Hall (1995) 20 41.1 8.09 32.45 14.3 30 Yes FAS
Heaton et al. (1995) 111 45.82 10.04 33.1 14.7 100 Yes FAS
Hildebrand (1996) 31 34.84 9.3 23.25 45 No CFL
Hodges et al. (1990) 14 40.1 73.1 13.3 50 Yes FAS
Johnson et al. (2006) 95 26.73 11.22 72.34 12.34 19 No CFL
Johnson et al. (2001) 38 39.58 8.88 40.8 17.29 63 No FAS
Johnson (2000) 145 42.28 14.25 78.74 16 43 Yes FAS
Johnstone et al. (1995) 20 37.8 29.42 12.35 80 No FAS
Kozora & Cullum (1995) 41 41.23 12.10 54.5 14.3 51 Yes FAS
43 45.76 14.26 64.6 14.2 37 Yes FAS
47 46.49 10.46 74.6 14.3 32 Yes FAS
43 40.74 11.9 83.8 14.9 37 Yes FAS
Kozora et al. (1999) 31 46.3 13.4 69.9 13.3 51 Yes FAS
Kramer et al. (2002) 27 41.0 14.0 72.82 15.67 Yes FAS
Kremen et al. (2003) 83 40.5 41.1 13.69 41 Yes FAS
Kuo (2001) 51 40.6 13.0 58.2 15.0 57 Yes FAS
Lafleche & Albert (1995) 20 51.90 10.99 76.2 14.7 45 Yes FAS
Lebowitz et al. (2001) 30 39.57 11.07 31.2 13.16 57 Yes FAS
Libon et al. (1994) 23 49.5 16.0 69.7 13.4 35 Yes CFL
14 43.5 13.3 81.0 12.4 29 Yes CFL
Lovejoy et al. (1999) 26 39.92 7.14 41 16 50 Yes CFL
Monsch et al. (1992) 53 41.2 12.5 71.2 13.6 32 Yes FAS
Munro et al. (2000) 17 45.18 14.14 66.94 13.27 53 Yes FAS
Myers & Rohling (2004) 29 49.9 10.2 38.6 13.43 50 Yes FAS
Nebes et al. (2002) 12 39.7 12.8 73.5 17.2 No FAS
Norris et al. (1995) 54 36.9 10.1 73.1 16.7 No FAS
40 40.5 7.8 19.4 13.6 No FAS
Nyberg et al. (1997) 39 42.51 9.77 77.3 13.6 No FAS
Owens et al. (2002) 10 45.2 13.8 27.7 17.3 0 No FAS
Rapport et al. (2001) 32 44.0 10.8 33.2 14.8 59 Yes FAS
Riccio et al. (2005) 30 40.73 11.62 21.09 14.38 43.3 No FAS
Rippeth et al. (2004) 60 40.1 9.6 34.4 13.2 50 No FAS
Rockers et al. (1996) 88 39.8 9.6 21 14.3 50 No FAS
Ross (2003) 125 38.1 7.9 20.1 31 Yes CFL
Ross et al. (2005) 60 38.88 7.72 20.43 22 No CFL
Rouleau et al. (2002) 5 51.8 73.8 13.2 20 Yes FAS
7 40.5 75.3 13.1 43 Yes FAS
Royall et al. (2005) 547 32.0 12.6 77.9 15.1 41.7 No CFL
Ruby (2000) 15 45.33 11.40 33.87 17.6 0 No FAS
Ruff et al. (1986) 120 39.7 40.5 14.0 50 Yes CFL
240 40.3 40.4 14.2 50 Yes CFL
Ryan et al. (1993) 67 42.64 10.50 35.3 13.8 31 Yes FAS
Salthouse et al. (1996) 259 37.3 49.98 15 37 No FAS
Saxton et al. (2000) 15 41.1 11.2 70.8 13.2 53 Yes FAS
Selnes et al. (1991) 309 45.7 12.7 31.0 16.1 100 Yes FAS
290 46.1 12.6 39.3 16.4 100 Yes FAS
97 45.9 12.3 48.5 16.7 100 Yes FAS
Simkins-Bullock et al. (1994) 19 43.58 9.63 52.6 15.6 53 Yes FAS
Simon et al. (2000) 65 43.0 11.0 31 12.8 40 No FAS
Spica (1995) 26 39.31 12.56 71.27 13.19 38 No CFL
Stowe (1996) 16 38.2 13.0 25.7 13.2 38 Yes FAS
Sumerall et al. (1997) 47 31 11.2 82.19 14.35 19 Yes CFL
Suter (1997) 75 38.87 10.67 23.54 13.5 33 Yes FAS
Svetina et al. (1999) 45 43.9 9.8 33 16.4 No CFL
Thomason (1997) 30 35.97 12.12 66.92 13.82 33 No FAS
Tombaugh et al. (1996) 12 38.5 12.0 37.5 7 Yes FAS
76 25.3 11.1 69.5 7 Yes FAS
75 22.4 8.2 87.5 7 Yes FAS
268 40.5 10.7 37.5 10.5 Yes FAS
292 35.6 12.5 69.5 10.5 Yes FAS
102 29.8 11.4 87.5 10.5 Yes FAS
242 44.7 11.2 37.5 17 Yes FAS
185 42.0 12.1 69.5 17 Yes FAS
46 37.0 11.2 87.5 17 Yes FAS
Tomer & Levin (1993) 26 39.2 11.8 55 13.2 Yes FAS
39 38.7 11.3 70 13.4 Yes FAS
19 38.6 10.4 82 13.7 Yes FAS
Troyer et al. (1997) 41 41.88 11.45 22.3 14.4 37 No FAS
54 41.26 10.9 73.3 13.2 50 No FAS
Troyer et al. (1998) 38 40.8 9.6 73.8 12.6 63 Yes FAS
37 42.7 11.4 54.4 13.9 46 No FAS
Vasudev (2000) 22 45.73 10.55 65.32 17.68 73 Yes FAS
Westervelt (2000) 17 49.06 16.0 51.06 16.18 24 Yes FAS
White et al. (1997) 15 50.3 7.2 37.7 14.5 100 No FAS
Woods & Troster (2003) 18 37.11 16.2 68.76 14.18 67 Yes FAS
Yuspeh (1994) 32 45.37 10.15 21.71 13.03 No FAS
Zakzanis et al. (2000) 35 39.77 9.04 43.9 12.6 31 Yes CFL
Zee et al. (1999) 45 36.6 13.1 63.1 13.6 24 Yes FAS
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