Development and Preliminary Evaluation of Psychometric Properties ...

Asian Nursing Research 9 (2015) 312e317

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Asian Nursing Research journal homepage: www.asian-nursingresearch.com

Research Article

Development and Preliminary Evaluation of Psychometric Properties of Symptom-Management Self-Efficacy Scale for Breast Cancer Related to Chemotherapy Shu-Yuan Liang, PhD, RN, 1, * Wei-Wen Wu, PhD, RN, 1 Chiu-Ya Kuo, MSN, RN, 2 Yu-Ying Lu, PhD, RN 1 1 2

College of Nursing, National Taipei University of Nursing and Health Sciences, Taipei, Taiwan Department of Nursing, Chiayi Chang Gung Memorial Hospital, Chiayi, Taiwan

a r t i c l e i n f o

s u m m a r y

Article history: Received 17 March 2015 Received in revised form 28 July 2015 Accepted 2 September 2015

Purpose: The purpose of this study was to develop and preliminarily evaluate the reliability and validity of the Symptom-Management Self-Efficacy ScaleeBreast Cancer (SMSES-BC) related to chemotherapy. Methods: The study included three stages. This paper presents the results of stage 2 and stage 3. In total, 34 items in the SMSES-BC were found during stage 1 from qualitative findings, a literature review, and expert suggestions; the 34 items were used for the psychometric properties test. Test-retest reliability and Cronbach a were assessed in the first sample, which included 45 participants for the pilot test (stage 2). The second sample, which included 152 patients, was used to assess the construct validity and concurrent validity (stage 3). Results: The pilot test results revealed a test-retest reliability of .73 (p < .001) and Cronbach a coefficient of .96 for the total scale. Three factors (managing chemotherapy-related symptoms, acquiring problem solving, and managing emotional and interpersonal disturbances) were identified from exploratory factor analysis. Correlation coefficient r was .40 (p < .001), which supported the association between SMSES-BC and the General Self-Efficacy Scale for concurrent validity. Conclusions: The study results demonstrate acceptable reliability and validity for the SMSES-BC that was developed for measuring symptom-management self-efficacy related to chemotherapy for patients with breast cancer. This study suggests further research to validate the construct of the SMSES-BC. Copyright © 2015, Korean Society of Nursing Science. Published by Elsevier. All rights reserved.

Keywords: drug therapy neoplasms self care self efficacy signs and symptoms

Introduction Breast cancer is one of the most common cancers in the world. Among all cancers affecting women in Taiwan, it ranks first in terms of prevalence and fourth in terms of mortality [1]. Chemotherapy is the standard treatment and has improved the survival rate of breast cancer patients [2,3]. Depending on the stage of diagnosis, the overall survival rate of breast cancer varies from 27% to 100% [3]. However, complications from chemotherapy overwhelm the patient's overall quality of life [4,5], such as leukopenia, edema and diarrhea [6], specifically the side effects of multiple chemotherapy regimens on the patients progressive tumor [7]. As our understanding of cancer extended, the treatment of advanced breast

* Correspondence to: Shu-Yuan Liang, Associate Professor, College of Nursing, National Taipei University of Nursing and Health Sciences, 365 Ming Te Road, Beitou, Taipei 112, Taiwan. E-mail address: [email protected]

cancer usually involves a combination of chemotherapy, hormone therapy, and target therapy [8]. Chemotherapy treatment has shifted from inpatient to outpatient care. Therefore, self-management is important for patients for controling symptoms related to chemotherapy at home [9]. Nevertheless, patients face various challenges related to the complications from chemotherapy because of the various symptom etiologies [10]. For example, pain may be caused by the cancer, and sleep disturbance may be caused by anxiety or the selected chemotherapy agents, which impede patients' capacity to selfmanage the side effects and further obstruct the treatment effects. Research has revealed that in performing self-management of side effects, patients usually confront many difficulties, including acquisition of accurate information and self-care skills if health professionals are busy at the clinic and situations in which the suggestions of health professionals are not suitable to the subject's condition. As a result, patients have difficulty developing self-care strategies [9,11,12].

http://dx.doi.org/10.1016/j.anr.2015.09.001 p1976-1317 e2093-7482/Copyright © 2015, Korean Society of Nursing Science. Published by Elsevier. All rights reserved.

S.-Y. Liang et al. / Asian Nursing Research 9 (2015) 312e317

Researchers have generally recommended education initiatives as a method for improving patient self-management behaviors related to chemotherapy; however, the execution of these strategies has not yet reached its potential [11,13]. In fact, the enhancement of a patient's knowledge and skill to improve patient behavior is limited. Patients may encounter various obstacles in conducting self-management behavior [9,12]. Indeed, traditional patient education may be insufficient in improving the management of side effects related to chemotherapy. Many notions assert that belief is crucial for individual health behavior [14e16]. Self-efficacy is the belief in an individual's ability to perform a specific task according to the specific components of the health behaviors being performing [16,17]. Particularly, selfefficacy influences persistence and effort level for an individual to overcome difficult circumstances. Self-efficacy is a potentially modifiable variable; by itself, it can provide the basis for effective interventions to improve health outcomes. Instruments have addressed self-efficacy among cancer patients but have focused on either the global impact of the disease [18,19] or particular aspects of a cancer diagnosis [20], breast cancer survivor [21], communication [22] or analgesic use [23]. The availability of a psychometrically robust instrument that can explore the potential role of selfefficacy may enhance researchers' understanding of the patients' capability beliefs and also the health outcomes of patients with breast cancer who have received chemotherapy. Particularly, the chemotherapy regimens keep changing as new chemotherapies and biotherapies are being developed. Therefore, novel symptom management assessment should be reflective of this trend. Our study aim was to develop and evaluate the reliability and validity of the Symptom-Management Self-Efficacy ScaleeBreast Cancer (SMSES-BC) in relation to chemotherapy. Methods The study was composed of three stages. Stage 1 focused on item generation, consisting of a qualitative interview that included 17 patients with breast cancer to identify main behaviors and tasks involved in the symptom management of chemotherapy. Stage 2 was a pilot test designed to evaluate the content validity and preliminary reliability of the initial scale developed from Stage 1. Stage 3 involved exploratory factor analysis, evaluating the concurrent validity of the SMSES-BC. This paper reports the results of stage 2 and stage 3. Approval to conduct the study was obtained from the institutional ethics committees of the participating agencies. All participants signed informed consent agreements. Pilot test (Stage 2) Instrument development A draft of the 33-item, self-administered SMSES-BC for patients with breast cancer undergoing chemotherapy was developed from an earlier qualitative study and literature review. This scale included 3 items regarding communicating about chemotherapyrelated concerns, 14 items concerning the measurement of chemotherapy-related symptoms, 7 items about managing emotional and interpersonal disturbances, and 9 items regarding acquiring relevant resources. Items in the scale were based on the categories that emerged from interview findings and the literature review to assess the main behaviors and tasks relevant to symptom-management self-efficacy. In the SMSES-BC scale, there are 11-point responses for various behaviors, ranging from 0 to 10, with 0 signifying not at all confident and 10 signifying complete confidence. A higher response score indicates higher perceived symptom-management self-efficacy.

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Six experts (2 oncology physicians, 3 oncology nursing experts, and 1 professor specializing in self-efficacy research) reviewed the initial version of the scale for relevance and clarity. Agreement on content validity ranged from .83 to 1.00; however, the experts suggested that two items for measuring communication about chemotherapy-related concerns be combined into one item. Additionally, these experts suggested that two more items be added: one item regarding managing chemotherapy-related symptoms and an item regarding acquiring relevant resources. Minor changes were made to the wording of some items according to panelist suggestions. Finally, 34 items of the scale were used in the pilot study. Sample The sample for stage 2 of the pilot study included 45 women (100%) from the oncology outpatient departments of two hospitals in the southern and northern areas of Taiwan. Participants had a breast cancer diagnosis that had received at least three courses of chemotherapy, were older than 18 years, and were conscious and able to sign the consent form. Participants' ages ranged from 30 years to 78 years old, with a mean age of 55.0 years (SD ¼ 11.0 years). Most patients were married (71.1%), lived with others (84.4%), had an educational level of primary school or below (42.2%), were either Buddhist (57.7%) or Taoist (22.2%), and were not working (60.0%). Around 77.3% of the participants had a diagnosis of metastatic breast cancer. Internal consistency Internal reliability was tested using the Cronbach a coefficient of the scale and subscales. The initial Cronbach a for the entire scale was .96. Cronbach a of each of the four initial subscales that were developed for evaluating the main four constructs derived from the Stage 1 interviews exceeded .70. The current results revealed a recommended standard of above .70 [24]. Test-retest reliability Stability was confirmed by test-retest with the initial pilot sample. The retest was performed approximately 2 weeks after the first completion of the scale. The current results of test-retest stability showed a significant correlation between the initial score and the retest score for all subscales (r ¼ .40, p < .001 to r ¼ .78, p < .001) and the total scale (r ¼ .73, p < .001). The results supported good test-retest reliability for the initial version of SMSES-BC [24]. Construct and concurrent validity (Stage 3) Sample The sample consisted of 152 outpatients with breast cancer recruited from two teaching hospitals in southern and northern areas of Taiwan. The sampling frame and inclusion criterion matched with those of stage 2 (the pilot study). Participants included 152 women (100%) diagnosed with breast cancer. Participants' ages ranged from 30 years to 78 years old, with a mean age of 54.3 years (SD ¼ 9.9 years). Most participants were married (71.7%), lived with others (77.6%), had an education level of primary school and below (24.3%), had a religion (87.5%), and were not working (66.5%). Participants were diagnosed breast cancer with a mean duration of 4.2 years (SD ¼ 5.4 years). Around 64.7% of the participants had a diagnosis of metastatic breast cancer. All patients underwent the treatment with various therapeutic agents included chemotherapy (65.2%), hormone therapy (37.6%), and target therapy (24.9%). Measures In addition to the 34-item SMSES-BC, the General Self-Efficacy Scale (GSES) was used to establish concurrent validity with the SMSES-BC. The GSES is a 10-item scale designed to evaluate the

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individual's beliefs of their ability in facing various life challenges. The GESE uses a 4-point Likert scale, ranging from 0 to 3, to assess patients' responses. The validity and reliability of GSES is wellestablished [25e27]. The content validity index ranged from .75 to 1.00 [27], and the relevance and clarity were scored by six panelist judges on a scale from 1 to 4; r for test-retest reliability ranged from .75 to .94, and the Cronbach a coefficient ranged from .92 to .93 for the Chinese version of GSES [25e27]. Item analysis Item analysis of the original 34-item scale was evaluated with the critical ratio and item-to-total correlation coefficient. The critical ratio for each item was analyzed via t test, and its results ranged from 3.76 to 5.39 (t ¼ 7.52e13.23, p < .001). The results revealed significant differences between the high-scoring group (with the highest 27.0% of scores) and low-scoring group (with the lowest 27.0% of scores) [28]. This finding supports the discriminatory power of the items in the SMSES-BC. Additionally, all item-total correlations were greater than .40, which is the standard for acceptability [29]. Results Construct validity of SMSES-BC The current study used exploratory principal component factor analysis to explore the potential constructs in the preliminary set of 34 self-efficacy items. Results of the Kaiser-Meyer-Olkin measure for sampling adequacy was .93; additionally, Barlett's test of

sphericity for appropriate assumptions was significant (c2 ¼ 3909.01, df ¼ 496, p ¼ .001), indicating that the factor analysis was fit. In this study, we used the orthogonal varimax rotation for the original principal component factor analysis. The results presented five factors with an eigenvalue of 1.00 or greater. These five factors were linked to 67.1% of the variance. All items were loaded onto at least one factor at the .40 level or above. Communalities for all items exceeded .50. To determine and clarify the number of items and factors to keep, several statistical processes and conceptual bases were considered [30]. Although six items that were originally conceptualized as measuring “acquiring and utilizing relevant resources” loaded onto four separate factors, these items could not be differentiated conceptually. Therefore, they were removed from the preliminary SMSES-BC. Furthermore, one item initially conceptualized as assessing the construct of managing emotional and interpersonal disturbance loaded onto factor 3. This item did not suit conceptually with the other items loading onto factor 3, which were used to assess the concept of managing chemotherapyrelated symptoms. Therefore, this item was also removed. Of the initial 34 items, 7 items were excluded, and 27 items remained. A final factor analysis was then completed on the 27 remaining items to approve the recommended factor structure. The results of the factor analysis extracted five factors with eigenvalues over 1. These five factors contributed to 70.2% of the variance (see Table 1). The results of the communalities in the factor analysis ranged between .62 and .78 (see Table 1). Items greater than .45 (cut-off),

Table 1 Components of Factors and factor loadings and Communalities in SMSES-BC (27 items) (N ¼ 152). Factor/Item

Factor 1 29. (MC) Managing hair loss 25. (MC) Managing peripheral problem of limbs 20. (MC) Preventing infection 23. (MC) Managing nail problem 17. (MC) Managing skin problem 22. (MC) Managing pain 27. (MC) Managing memory loss Factor 2 1. (ME) Managing social activity disturbance 2. (ME) Managing emotional distress 6. (ME) Managing interpersonal stress 11. (ME) Seeking place for emotion 32. (AR) Obtaining support from surrounding people 30. (ME) Managing interpersonal isolation Factor 3 15. (MC) Managing sleeping problem 3. (MC) Managing palpitation 8. (MC) Managing nausea and vomiting 16. (MC) Managing eating problem 10. (MC) Managing endocrine problem 5. (MC) Managing fatigue 34. (MC) Managing gastrointestinal problem Factor 4 12. (CC) Actively talk with health professional about the side effects of chemotherapy before treatment 14. (CC) Actively talk with health professional about my side effects of chemotherapy after treatment 26. (CC) Actively talk with health professional about the management of side effects of chemotherapy 13. (MC) Managing the problems related to oral mucosa Factor 5 24. (AR) Obtaining support from social group 28. (AR) Obtaining internet resources to manage the problems related to chemotherapy 31. (AR) Managing the work problems related to chemotherapy Eigenvalue Percentage of variance explained Cumulative percentage

h2

Factor/Factor loading 1

2

3

4

5

0.79 0.67 0.66 0.61 0.60 0.49 0.49

e 0.32 0.28 0.37 0.23 0.39 e

0.17 0.22 0.32 0.25 0.31 0.43 0.47

e 0.33 0.26 0.42 0.48 0.30 0.10

0.27 0.15 0.17 0.16 e e 0.39

0.73 0.73 0.70 0.77 0.74 0.67 0.62

0.21 0.18 0.19 0.24 0.33 0.55

0.71 0.70 0.67 0.64 0.61 0.45

0.15 0.44 0.34 0.20 0.14 0.17

0.11 0.16 0.22 0.28 0.47 0.24

0.31 e 0.32 0.23 0.15 0.31

0.68 0.74 0.75 0.64 0.74 0.69

0.14 0.19 0.35 0.17 0.42 0.13 0.45

0.17 0.27 0.25 0.43 e 0.58 0.44

0.77 0.68 0.67 0.64 0.59 0.54 0.46

0.23 0.13 e 0.35 0.32 0.22 0.40

0.17 0.19 0.13 e e 0.15 e

0.72 0.62 0.65 0.75 0.64 0.71 0.77

0.17 0.11 0.30 0.36

0.19 0.17 0.24 0.36

0.13 0.22 0.27 0.21

0.79 0.79 0.61 0.60

0.27 0.24 0.30 0.14

0.78 0.76 0.68 0.68

0.14 0.19 0.26 4.29 15.9 15.9

0.16 0.34 0.19 4.25 15.8 31.7

0.14 e 0.36 4.24 15.7 47.4

0.29 0.18 0.23 3.75 13.9 61.2

0.76 0.68 0.60 2.42 9.0 70.2

0.72 0.65 0.64

Note. AR ¼ acquiring relevant resources; CC ¼ communicating about chemotherapy related concerns; h2 ¼ communality; MC ¼ managing chemotherapy related symptoms; ME ¼ managing emotional and interpersonal disturbance; SMSES-BC ¼ Symptom-Management Self-Efficacy Scale-Breast Cancer. Underlined values mean factor loadings.


which loaded on more than one factor (see Table 1), were located on the factor with the finest conceptual properties of the original constructs [28,30]. The results of the final factor analysis showed that items originally developed to assess the concept of managing chemotherapyrelated symptoms continued to load separately on two different factors (7 items loaded on factor 1 and the other 7 items loaded on factor 3). These two factors were combined to create one scale assessing managing chemotherapy-related symptoms. Moreover, the association between these two factors indicated intercorrelations (Pearson's r ¼ .79, p < .001), suggesting a conceptual alliance. Except for item 32, all items loading on factor 2 echoed the dimension of managing emotional and interpersonal disturbance. Item 32 was initially developed to evaluate the concept of acquiring and utilizing relevant resources (AR). This item loaded on both managing emotional and interpersonal disturbance (factor 2) and communicating about chemotherapy-related concerns (factor 4), with factor loading over .45. Therefore, item 32 was kept as part of communicating about chemotherapy-related concerns (factor 4). Moreover, except for item 13, all items loading on factor 4 were initially developed to evaluate the concept of communicating about chemotherapy-related concerns. Item 13 was initially developed to evaluate the concepts of managing chemotherapy-related symptoms, and its original conception was to measure self-management of the oral mucosa because such management was an important issue in chemotherapy. Therefore, item 13 was kept as part of managing chemotherapy-related symptoms. Three items that were initially developed to evaluate the concept of acquiring relevant resource loaded above .45 on factor 5. Finally, factor 4 and factor 5 were combined to create one scale, which was renamed acquiring problem-solving. These factors were integrated because of the small number of items of the two separate factors and because items that initially measured AR crossloaded on factor 4, such as

item 32. Nevertheless, communalities of all items that loaded on factor 4 and factor 5 were above .6, suggesting that these items revealed communal factor variance [29]. Additionally, the association between these two factors indicated intercorrelation (Pearson's r ¼ .63, p < .001), further indicating that these two factors were conceptually linked. The names of the subscales and associated items that were included in the revised 27 items of the SMSES-BC are presented in Table 2. The revised 27 items were assessed using confirmatory factor analysis. The standardized factor loading for each item ranged between .58 and .80 for factor 1, between .59 and .84 for factor 2, and between .71 and .84 for factor 3. The results indicated that the latent variable can be measured by the items [31]. Internal consistency of the revised 27-item SMSES-BC Internal consistency was evaluated for the 27-item scale and subscales of SMSES-BC (Table 3). The internal reliability for the total scale was .96. The Cronbach a for all subscales ranged from .88 to .95. Moreover, the item-total correlation of the total scale and each subscale was greater than .40. Concurrent validity of the revised 27-item SMSES-BC The SMSES-BC significantly correlated with the GSES (r ¼ .40, p < .001). Additionally, all subscales of the SMSES-BC significantly and positively correlated with the GSES (r ¼ .37e.40, p < .001) (Table 4). Discussion The purpose of this study was to develop and preliminarily evaluate a scale for measuring symptom-management self-efficacy of patients with breast cancer who had received chemotherapy. The

Table 2 Names of Subscales and Item Descriptions for Revised SMSES-BC. Item Subscale 1 (7 items): Acquiring problem-solving (AP) 9. Actively talk with health professional about the side effects of chemotherapy before treatment 11. Actively talk with health professional about my side effects of chemotherapy after treatment 18. Obtaining support from social group (e.g., peer group, church member) 20. Actively talk with health professional about the management of side effects of chemotherapy 22. Obtaining internet resources to manage the problems related to chemotherapy 25. Managing the work problems related to chemotherapy (e.g., asking for sick leave) 26. Obtaining support from surrounding people (e.g., health professional, family, friend) Subscale 2 (15 items): Managing chemotherapy-related symptoms (MC) 3. Managing palpitations (e.g., tachycardia) 4. Managing fatigue (e.g., tiredness, weakness) 6. Managing nausea and vomiting 7. Managing endocrine problems (e.g., night sweat, flush) 10. Managing the problems related to oral mucosa (e.g., mucositis, cheilosis) 12. Managing sleeping problems (e.g., insomnia, light sleeping) 13. Managing eating problems (e.g., difficulty in swallowing, parageusia, poor appetite) 14. Managing skin problems (e.g., darkening, decortication, skin rash, itching) 15. Preventing infection (e.g., anemia, blood cells decreasing) 16. Managing pain (e.g., bone pain, sore muscles, spasm) 17. Managing nail problems (e.g., darkening, deformation, burst) 19. Managing peripheral problems of limbs (e.g., numbness, rigid) 21. Managing memory problems (e.g., short memory, forgetful) 23. Managing hair loss 27. Managing gastrointestinal problems (e.g., distention, constipation, diarrhea) Subscale 3 (5 items): Managing emotional and interpersonal disturbance (ME) 1. Managing social activity disruptions (e.g., stopping gathering, stopping gossip) 2. Managing emotional distress (e.g., feeling down, powerless, worry, fear) 5. Managing interpersonal stress (e.g., stress from people paying attention) 8. Seeking place for emotion (e.g., religion, painting, patchwork, book) 24. Managing interpersonal isolation Note. SMSES-BC ¼ Symptom-Management Self-Efficacy ScaleeBreast Cancer.

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Table 3 Reliability of Revised SMSES-BC (N ¼ 152). Subscales

No. of items

Standardized item a

Corrected item-total correlation range

1 2 3 Total scale

7 15 5 27

.88 .95 .88 .96

.57e.73 .58e.81 .65e.78 .56e.81

Note. SMSES-BC ¼ Symptom-Management Self-Efficacy ScaleeBreast Cancer.

Table 4 Relationships between Total Scale and Subscales of SMSES-BC and GSES (N ¼ 152). Subscales 1. Acquiring problem-solving 2. Managing chemotherapy-related symptoms 3. Managing emotional and interpersonal disturbance Total scale

No. of items

Pearson's r

p

7 15

.40 .37

.001 .001

5

.40

.001

27

.40

.001

Note. GSES ¼ General Self-Efficacy Scale; SMSES-BC ¼ Symptom-Management SelfEfficacy ScaleeBreast Cancer.

final SMSES-BC is a 27-item self-administered scale. The results of Cronbach a and test-retest reliability showed that the SMSES-BC is a scale with internal consistency, yielding stable scores if measured repeatedly [29,30,32,33]. The results of construct and concurrent validity for the preliminary evaluation of the SMSES-BC also demonstrated that the scale was acceptable. For construct validity, results of the factor analysis revealed that the scale was naturally multidimensional. Three factors emerged from the factor analysis, including acquiring problem-solving, managing chemotherapy-related symptoms, and managing emotional and interpersonal disturbances. Researchers have suggested that for an exploratory principal component factor analysis, a sample size of 150e200 and a factor loading of at least .45 are required [28]. This study was conducted in accordance with these criteria, and the assumptions for a factor analysis also fit the data. The current results supported the appropriate construct validity. Nevertheless, concurrent validity was demonstrated by significant correlations between the SMSES-BC and GSES. These relationships are robust. GSES is the “gold standard” of criterionreferenced assessment for many studies related to the development of the self-efficacy scales [34,35]. Essentially, the current results supported the criterion validity of the SMSES-BC. The SMSES-BC can be used to identify specific behavior tasks performed by patients in managing individual symptoms related to chemotherapy. Particularly this scale is designed specifically to assess the symptom management required during chemotherapy. For clinical practice, the message emerged from this scale may provide healthcare providers with an understanding of the challenges that individual patients face and encourage a valuable discussion regarding symptom management. Furthermore, this scale is particularly important for clinicians to assess the extent to which a patient reports lower levels of confidence in being able to perform these self-management behaviors, so that such difficulties can be the target of appropriate health professional intervention. For research, the scale provides an effective measurement for understanding an individual's belief in his or her ability to manage symptoms related to chemotherapy and for predicting patient selfcare behaviors [16]. The advantage of the SMSES-BC is that the scale originated from patients with breast cancer. This scale was developed and tested by means of patients with breast cancer who had received chemotherapy. Patients were therefore more likely to provide accurate

measurements of their beliefs in competencies involved in managing symptoms related to chemotherapy. Therefore, this scale has inherent content validity. Furthermore, the items in this scale reflect multiple aspects of tasks, behaviors, and situations associated with symptom-management for chemotherapy identified by patients. This scale provides a holistic perspective in assessing an individual's beliefs in relation to self-management of chemotherapy symptoms. The preliminary development of the SMSES-BC is designed for use among a wide range of patients with breast cancer, varying in age, stage, and treatment modalities. This study suggests further research to validate the construct of the SMSES-BC. The development of SMSES-BC is limited by the preliminary nature of the analysis. As such, more research utilizing confirmatory factor analysis, for example, structural equation modeling and convergent and discriminant validity, is needed to further investigate the potential importance symptom-management self-efficacy. Conclusion This study provides initial evidence of the reliability and validity of the SMSES-BC. The reliability evaluations acquired in this 27item scale indicated appropriate internal consistency. Concurrent validity of the SMSES-BC was also supported. Further validation is suggested; however, based on the results presented from the present study, the scale is suitable for measuring a variable that may be an important factor in achieving and maintaining self-management of symptoms caused by chemotherapy in patients with breast cancer. The SMSES-BC can help professionals assess the patients' capability beliefs in terms of self-efficacy in relation to selfmanagement of chemotherapy. Conflicts of interest The authors declare no conflict of interest. Acknowledgments This study was supported by the National Science Council in Taiwan (NSC 99-2314-B-227 003-MY3). References 1. Bureau of Health Promotion. Taiwan Cancer Registry. [Internet]. 2009 [cited 2013 Aug 26]. Available from: http://www.mohw.gov.tw/cht/DOS/Statistic. aspx?f_list_no¼312&fod_list_no¼2616 2. Moulder S, Hortobagyi GN. Advances in the treatment of breast cancer. Clin Pharmacol Ther. 2008;83:26e36. http://dx.doi.org/10.1038/sj.clpt.6100449 3. American Cancer Society. Breast cancer facts and figures. [Internet]. Atlanta (GA): Author; 2007e2008 [cited 2013 Aug 26]. Available from: http://www. cancer.org/acs/groups/content/@nho/documents/document/bcfffinalpdf.pdf 4. Kim HJ, Barsevick AM, Tulman L. Predictors of the intensity of cluster symptoms in patients with breast cancer. J Nurs Scholarship. 2009;41:158e65. http://dx.doi.org/10.1111/j.1547-5069.2009.01267.x 5. Byar KL, Berger AM, Bakken SL, Cetak MA. Impact of adjuvant breast cancer chemotherapy on fatigue, other symptoms, and quality of Life. Oncol Nurs Forum. 2006;33:E18e26. http://dx.doi.org/10.1188/06.ONF.E18-E26 6. Tsai SM, Lin CY, Wu SH, Hou LA, Ma H, Tsai LY, et al. Side effects after docetaxel treatment in Taiwanese breast cancer patients with CYP3A4, CYP3A5, and ABCB1 gene polymorphisms. Clin Chim Acta. 2009;404:160e5. http://dx.doi.org/10.1016/j.cca.2009.03.038 7. Park IH, Lee KS, Ro J. Effects of second and subsequent lines of chemotherapy for metastatic breast cancer. Clin Breast Cancer. 2015;15:e55e62. http://dx.doi.org/10.1016/j.clbc.2014.09.001 8. Bourdeanu L, Liu EA. Systemic treatment for breast cancer: chemotherapy and biotherapy agents. Semin Oncol Nurs. 2015;31:156e62. http://dx.doi.org/10.1016/j.soncn.2015.02.003 9. Royer HR, Phelan CH, Heidrich SM. Older breast cancer survivors' symptom beliefs. Oncol Nurs Forum. 2009;36:463e70. http://dx.doi.org/10.1188/09.ONF.463-470

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