Additional Construct Validity of

Journal of Nursing Measurement, Vol. 7, No. 1, 1999 © 1999 Springer Publishing Company

Additional Construct Validity of the Schwartz Cancer Fatigue Scale Anna Schwartz, RN, PhD, ARNP Paula Meek, RN, PhD The purpose of this article is to report the results of additional construct validity testing of the Schwartz Cancer Fatigue Scale. Latent variable modeling was used to determine the best fit of the data to the model. Testing with a heterogeneous sample (n = 303) did not support the proposed model. Using exploratory techniques a six-item, two-factor scale was formed which demonstrated that all measures of fit were consistently strong, and that the standardized solution factors loaded strongly. Reliabilities for the total scale and subscales were all greater than 0.80. These results provide preliminary support for the reliability and validity of the two-factor model of the six-item Schwartz Cancer Fatigue Scale.

Fatigue is a common sensation experienced by people everyday to varying degrees. Fatigue is a key symptom associated with depression, cancer, multiple sclerosis, arthritis, renal disease, and HIV infection. Many medical treatments and pharmacological treatments induce fatigue. Because fatigue is such a widespread and pervasive problem of interest to many researchers, its measurement needs to be reliable and valid. In healthy persons, fatigue is considered protective with a rapid onset, short duration, and rapid resolution (McFarland, 1971; Manu, Lane, & Matthews, 1988). Persons being treated for cancer experience the sensation of fatigue as a significant symptom that interferes with normal activities, is not relieved with rest, and has a major impact on ones quality of life (Massias, Yeager, Dibble, & Dodd, 1997; Nail & Jones, 1995; Nail & Winningham, 1995). It is estimated that between 40%-100% of cancer patients experience cancer-related fatigue (Irvine, Vincent, Bubela, & Thompson, 1991; Nail & Winningham, 1995; Vaders & Kemp, 1995; Winningham et al., 1994). Cancer patients describe the experience of cancer-related fatigue to be significantly different and more severe than the fatigue they experienced before treatment (Nail & Winningham, 1995;

From the University of Washington, School of Nursing (A. Schwartz) and the University of Arizona,

College of Nursing (P. Meek).

,, .05 0.917 0.883 0.953 0.985 0.949

Chi-square Bentler-Bonnett Normed Bentler-Bonnett Non-normed Comparative Fit Index (CFI) Liseral GFI Liseral AGFI

TABLE 4. Itenn Loadings on Ea .98 and AGFI > .94) supported the construct validity of the SCFS and the two-factor solution. Although post hoc model fitting has been criticized (Fornell, 1983), others have argued for the substantive meaning of a sensitivity analysis that takes into consideration both the practical and statistical significance of the model (Joreskog, 1982; Tanaka & Huba, 1984). The decision regarding the inclusion and exclusion of parameters involved consideration of both statistical and substantive significance to the model. The exploratory nature of this sensitivity analysis has yielded a parsimonious model that needs further testing to substantiate these results. Interestingly, four of the six items that remain in the SCFS were the strongest items in content validity (Schwartz, 1998a). The items "tired" and "listless" had 100% agreement between both cancer patients and oncology nurse experts. Cancer patients had 100% agreement on the relevancy of the items "worn-out" and "helpless". This recursive model may help explain the cognitive fatigue that may develop as a result of physical fatigue (Cimprich, 1992a; 1992b). The model proposes that the physical dimension of fatigue contributes to the perceptual dimension of fatigue. Being "overcome" by fatigue and experiencing "difficulty thinking" may be a direct sequela of physical fatigue, or the result of an accumulation of fatigue (as in Aistars' [1987] Organizing Framework). Although this model suggests a direct relationship from the physical dimension to the perceptual dimension, further testing is needed. The two factor model subsumes items from the physical, emotional, and cognitive dimensions of the original model. With only six items considered, the three items represented in the perceptual dimension include items from the initially hypothesized emotional and cognitive dimensions. All the items from the temporal dimension were eliminated which may in part reflect a problem in the stem of the question pertaining to the temporal items. However, the rapid changes in cancerrelated fatigue observed in patients receiving cancer treatment (Nail & Jones, 1995; Nail & Winningham, 1995) makes measurement of the temporal dimension of cancer-related fatigue problematic. Further testing of the discriminate validity of this model may determine the level, or severity of cancer-related fatigue that is experienced before the perceptual feelings become evident. Being able to differentiate the patient for whom physical fatigue is a greater problem than perceptual fatigue, or vice versa, will be important as interventions are developed to reduce the perceptual and physical feelings of cancer-related fatigue.

Construct Validity of the SCFS

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LIMITATIONS AND RECOMMENDATIONS FOR FUTURE STUDY The elimination of the temporal subscale, while statistically sound, may pose theoretic constraints to the assessment of acute and chronic fatigue. Simply modifying the time frame in the instructions from 2 to 3 days to past 24 hours or past week may address the temporal concerns of researchers and clinicians. The SCFS has not been tested using different time frames. Further studies are needed to address the psychometrics of the SCFS using different time frames, sensitivity to change over time, ability of the measure to discriminate fatigue experienced by patients receiving different treatments and the ability of the instrument to measure fatigue in pediatric patients.

CONCLUSIONS This analysis dramatically restructured the SCFS and added strong evidence of construct validity. The new SCFS is a parsimonious measure of cancer-related fatigue that may prove useful in both a clinical and research setting. Results of factor analysis and internal consistency reliability provide preliminary support for the sixitem, two-dimensional model of the SCFS that has relied on knowledge of substantive and theoretical research in cancer-related fatigue to specify the best fitting model. Additional testing is needed to determine discriminate validity and to provide further support for the construct validity of the two-dimensional SCFS. As with all rigorous research, particularly with construct validity, replication work is needed to confirm or refute these findings. Despite this, the SCFS is psychometrically strong with excellent content validity, reliability, and evidence of construct validity. While most measures of cancer-related fatigue are incorporated in instruments intended to measure other aspects of functioning, the SCFS is the only brief measure developed specifically to measure cancer-related fatigue. The brevity and multidimensionality of this instrument makes it attractive for use with a population of patients known to be affected by fatigue.

REFERENCES Aistars, J. (1987). Fatigue in the cancer patient: A conceptual approach to a clinical problem. Oncology Nursing Forum, 12, 122-127. Rentier, P. M. (1989). EQS Structural Equations Program Manual. Los Angeles: BMDP Statistical Software, Inc. Bentler, P. M. (1995). EQS Structural Equations Program Manual. Encino, CA: Multivariate Software, Inc. Byrne, B. M. (1994). Structural equation modeling with EQS and EQS/Windows. Thousand Oaks, CA: Sage Publications. Cella, D. (1997). The Functional Assessment of Cancer Therapy-Anemia (FACT-An) Scale: A new tool for the assessment of outcome in cancer anemia and fatigue. Seminars in Hematology, 34(Supp\. 2), 13-19. Cimprich, B. (1992a). A theoretical perspective on attention and patient education. Advances in Nursing Science, 14, 39-51.

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Cimprich, B. (1992b). Attentional fatigue following breast cancer surgery. Research in Nursing and Health, 15, 199-207. Fobair, P., Hoppe, R. T., & Bloom, L. (1986). Psychosocial problems among survivors of Hodgkin's disease. Journal of Clinical Oncology, 4, 805-814. Fornell, C. (1983). Issues in the application of covariance structure analysis: A comment. Journal of Consumer Research, 9, 443-448. Hoyle, R. H. (1995). Structural equation modeling: Concepts, issues and applications. Thousand Oaks, CA: Sage Publications. Irvine, D. M., Vincent, L., Bubela, N., Thompson, L., & Graydon, J. (1991). A critical appraisal of the research literature investigating fatigue in the individual with cancer. Cancer Nursing, 14, 188-199. Joreskog, K. G. (1982). Analysis of covariance structures. In C. Fornell (Ed.), A second generation of multivariate analysis: Vol. 1. Methods (pp. 200-242). New York: Praeger. Joreskog, K. G., & Sorbom, D. (1993). Fitting and testing. LisrelS: Structural Equation modeling with the SIMPLIS command language (pp. 122-123). Chicago: Scientific Software International. Kim, J., & Mueller, C. W. (1978). Factor analysis: Statistical methods and practical issues. Beverly Hills, CA: Sage. Long, J. S. (1983). Confirmatory factor analysis. Thousand Oaks, CA: Sage Publications. Manu, P., Lane, T. J., & Matthews, D. A. (1988). The frequency of the chronic fatigue syndrome in patients with symptoms of persistent fatigue. Annals of Internal Medicine, 109, 554-556. Massias, D. K. H., Yeager, K. A., Dibble, S. L., & Dodd, M. J. (1997). Patients' perspectives of fatigue while undergoing chemotherapy. Oncology Nursing Forum, 24, 43-48. McCorkle, R. (1981). Non-obtrusive measures in clinical nursing research. In R. Tiffany (Ed.), Cancer Nursing Update. Proceedings of the second international cancer nursing conference. London: Balliere Tindall. McFarland, R. (1971). Fatigue in industry: Understanding fatigue in modern life. Ergonomics, 14, 1-10. McNair, D. M., Lorr, M., & Droppleman, L. F. (1992). Profile ofMoodStates manual. San Diego: Educational and Industrial Testing Service. Nail, L. M., & Jones, L. S. (1995). Fatigue as a side effect of cancer treatment: Impact on quality of life. Quality of Life-A Nursing Challenge, 4, 8-13. Nail, L. M., & Winningham, M. L. (1995). Fatigue and weakness in cancer patients: The symptom experience. Seminars in Oncology Nursing, 11, 272-278. Pearson, P. G., & Byars, G. (1956). The development and validation of a check list measuring subjective fatigue (Report No. 56-115). Randolph AFB, TX: USAF School of Aviation. Piper, B. F. (1997). Measuring Fatigue. In M. Frank-Stromborg & S. J. Olsen (Eds.), Instruments for Clinical Health-Care Research (pp. 482-496). Boston: Jones and Bartlett Publishers. Piper, B. F., Dibble, S. L., Dodd, M. J., Weiss, M. C., Slaughter, R. E., & Paul, S. M. (1998). The revised Piper Fatigue Scale: Psychometric evaluation in women with breast cancer. Oncology Nursing Forum, 25, 677-684. Piper, B., Lindsey, A., & Dodd, M. (1987). Fatigue mechanisms in cancer patients: Developing nursing theory. Oncology Nursing Forum, 14, 17-23.

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Post-White, J., & Schroeder, L. (1997, January, 23-25). Factors influencing breast cancer survivors 'fatigue, emotional state and immunefunction and quality of life. Presented at the American Cancer Society National Conference on Cancer Nursing Research, Panama City, FL. Schwartz, A. L. (1998). Patterns of exercise and fatigue in physically active cancer survivors. Oncology Nursing Forum, 25, 485-491. Schwartz, A. L. (1998a). Reliability and validity of the Schwartz Cancer Fatigue Scale. Oncology Nursing Forum, 25, 711-718. Stommel, M., Wang, S., Given, C. W., & Given, B. (1992). Focus on psychometrics: Confirmatory factor analysis (CFA) as a method to assess measurement equivalence. Research in Nursing and Health, 15, 399-405. Tabachnick, B. G., & Fidell, L. S. (1996). Using Multivariate Statistics (3rd ed.). New York: Harper Collins College Publishers. Tanaka, J. S., & Huba, G. J. (1984). Confirmatory hierarchical factor analyses of psychological distress measures. Journal of Personality and Social Psychology, 46, 621-635. Vaders, L., & Kemp, E. (1995). A meta-analysis of studies of fatigue in patients with breast cancer (Abstract 163). Oncology Nursing Forum, 22, 387. Winningham, M. L., Nail, L. M., Burke, M. B., Brophy, L., Cimprich, B., Jones, L. S., Pickard-Holley, S., Rhodes, V., St. Pierre, B., Beck, S., Glass, E. C., Mock, V., Mooney, K. H., & Piper, B. (1994). Fatigue and the cancer experience: The state of the knowledge. Oncology Nursing Forum, 27, 23-36. Yoshitake, H. (1971). Relations between the symptoms and the feelings of fatigue. Ergonomics, 14, 175-186. Acknowledgment. Preparation of this manuscript was funded in part by a University of Utah Graduate Research Fellowship, NIH T32 NR07071-04, and F32 NR07159-0.

SCWARTZ CANCER FATIGUE SCALE (SCFS-6) The words and phrases below describe different feelings people associate with fatigue. Please read each item and circle the number that indicates how much fatigue has made you feel in the past 2 to 3 days.

1 = not at all 2 = a little 3 = moderately 4 = quite a bit 5 = extremely Tired Difficulty Thinking Overcome Listless Worn Out Helpless

1 1 1 1 1 1

2 2 2 2 2 2

3 3 3 3 3 3

4 4 4 4 4 4

5 5 5 5 5 5