Support Care Cancer (2015) 23:1907–1916 DOI 10.1007/s00520-014-2554-z

ORIGINAL ARTICLE

Participation in questionnaire studies among couples affected by breast cancer Helene Terp & Nina Rottmann & Pia Veldt Larsen & Mariët Hagedoorn & Henrik Flyger & Niels Kroman & Christoffer Johansen & Susanne Dalton & Dorte Gilså Hansen

Received: 8 July 2014 / Accepted: 30 November 2014 / Published online: 10 December 2014 # Springer-Verlag Berlin Heidelberg 2014

Abstract Objective Participation bias may be a problem in couplebased psychosocial studies. Therefore, it is important to investigate the characteristics associated with participation. The aim of this study was to analyze whether participation in a longitudinal psychosocial questionnaire study among couples affected by breast cancer was associated with socioeconomic, breast cancer-specific, and other health-related characteristics of the patients and partners. Methods The analyzes are based on 2254 couples who were invited to participate in a nationwide survey on psychosocial adjustment among couples dealing with breast cancer. H. Terp (*) : N. Rottmann : P. V. Larsen : D. G. Hansen National Research Center of Cancer Rehabilitation, Research Unit of General Practice, Institute of Public Health, University of Southern Denmark, J.B. Winsløws Vej 9A, 5000 Odense, Denmark e-mail: [email protected] M. Hagedoorn Health Sciences/Health Psychology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands H. Flyger Department of Breast Surgery, Herlev Hospital, Herlev, Denmark N. Kroman Department of Breast Surgery, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark N. Kroman The Danish Breast Cancer Cooperative Group, DBCG Secretariat, Rigshospitalet, Copenhagen, Denmark

Participating couples (N=792) were compared with nonparticipating couples (N=1462) with regard to socioeconomic and health-related characteristics obtained from nationwide clinical and administrative registers. Results Associations were seen between various socioeconomic variables and couple participation. The patient characteristics older age (OR = 0.15 [95 % CI = 0.07– 0.55]), low education (OR = 1.95 [95 % CI = 1.46– 2.68]), disability pension (OR =0.59 [95 % CI=0.39– 0.55]), or non-western ethnicity (OR=0.36 [95 % CI= 0.15–0.82]) reduced couple participation. The partner characteristics older age (OR = 0.23 [95 % CI = 0.15– 0.43]), low education (OR = 1.67 [95 % CI = 1.25– 2.22]), receiving disability pension (OR = 0.46 [95 % CI = 0.25–0.82]), non-western ethnicity (OR = 0.17 [95 % CI = 0.06–0.49]), or high morbidity (OR = 0.76 [95 % CI=0.60–0.96]) also reduced couple participation. Furthermore, couples with low income (OR=1.49 [95 % CI=1.16–1.95]) had reduced participation. No associations were found between couple participation and breast cancer-related variables. Conclusions Socioeconomic characteristics of patients and partners, and morbidity of partners may influence participation in couple-based psychosocial breast cancer research. Breast cancer-related characteristics do not seem to influence participation. Keywords Cancer . Oncology . Couples and breast cancer . Participation . Psychosocial . Socioeconomic

C. Johansen Unit of Survivorship, Danish Cancer Society Research Center, Copenhagen, Denmark

Background

C. Johansen : S. Dalton Finsencenteret, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark

Every year, many women in the western world are diagnosed with breast cancer [1]. Breast cancer has a big influence on the women’s lives and wellbeing, but also their partners are

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affected by this life-changing experience [2–4]. This is reflected by partners of patients with breast cancer having increased use of general practice for somatic and psychosocial symptoms [5], and having increased risk of hospitalization with an affective disorder [6]. To gain knowledge on the challenges of breast cancer patients and their partners meet, research on the psychosocial aspects among couples facing cancer is increasing. In recent years, it has generally become more difficult to achieve high participation rates in questionnaire studies [7], and it is particularly difficult to obtain high response rates in couple-based studies [8]. In couplebased research, participation is dependent on both patient and partner agreeing to participate. A systematic review from 2013 found that more than half of the studies on couples coping with cancer did not report the response rates. In the studies reporting response rates, the rates ranged between 25 and 90 %, with a mean of 58 % and a standard deviation of 17 % [8]. Low participation rates do not necessarily introduce bias, but it is important to assess the influence of nonparticipation bias [7, 9]. It is reasonable to expect that participants in couple-based research do not fully represent all eligible couples. Factors related to both patient and partner may influence the couple’s decision on participation. In particular, studies have suggested that ethnicity [10], income [11], and psychosocial characteristics [11, 12] may influence participation in psychosocial couple-based research. However, none of the studies had information on all non-participating couples. In Denmark, nationwide registers contain information on all citizens. Registration of information uses a unique person identifier, enabling linkage between data sources and almost complete coverage and follow-up [13]. Thus, it is possible to retrieve socioeconomic and health-related information regarding both patients and partners, irrespective of participation status. The aim of this study was to analyze whether participation in a longitudinal psychosocial questionnaire study among couples affected by breast cancer was associated with socioeconomic, breast cancer-specific, and other health-related characteristics of the patients and partners.

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Study population Inclusion in cohort All residents of Denmark have a personal identification number, a unique 10-digit number assigned by the Civil Registration System [13], which permits accurate linkage of information from registers. Based on the Civil Registration System and the clinical database of the Danish Breast Cancer Cooperative Group (DBCG) [14], a nationwide cohort of women diagnosed with breast cancer and their cohabiting male partners was established, the Danish Couples and Breast Cancer Cohort (DCBCC). Couples were included in DCBCC from July 2011 to August 2012. A couple was eligible if the patient was female, ≥18 years, Danish resident, had undergone surgery for primary invasive breast cancer ≤4 months prior to being invited to the study, and was cohabiting with a male partner (≥18 years). Cohabiting with male partner was defined as being married and cohabiting, or by fulfilling all of the following criteria: (1) male at same residence; (2) male≥18 years old; (3) age difference≤15 years; and (4) only one male meets criteria. Each month from March 2011 to May 2012, we received information on patients recently registered in DBCG and assessed the patient for eligibility for the questionnaire study. The patient’s vital status, residence, and partner status were checked using the Civil Registration System. If the patient was registered as not wanting research-related inquiries, the couple was excluded (Fig. 1). Invitation to questionnaire study Invitations to participate in the questionnaire study were sent to all eligible patients by postal mail. Patients were asked to invite their partner to participate. The mailed invitation package included a letter of invitation to the patient, a leaflet with further information on the study, the patient baseline questionnaire, the partner baseline questionnaire, two informed consent forms, two prepaid return envelopes, and a declination form that the couple was encouraged to return if they did not wish to participate. In addition to a box stating “do not wish to participate”, the form had space to give reasons for the decision in free text. Two reminders were sent with an interval of 4 weeks each. The invitation was to a questionnaire study with an anticipated follow-up period of 5 years, where the participants could expect a total of five survey rounds.

Methods Questionnaire In this study, a register-based analysis of participation in a population-based psychosocial questionnaire study of couples affected by breast cancer is conducted. Through nationwide registers covering cancer-related, socioeconomic, and healthrelated characteristics, data were obtained for all eligible patients and partners.

Both the patient and the partner baseline questionnaires comprised the following main constructs: quality of life, work ability, depressive symptoms, body image, physical symptom experience, illness perception, dyadic coping, sexual functioning, relationship functioning, and partner’s involvement in

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Fig. 1 Flow-chart of a national population-based psychological study of couples affected by breast cancer

breast cancer. The length was 26 pages. Since this paper does not consider the results from the survey, the content of the questionnaires will be described in further detail in later publications.

study. Couples were regarded as participants if both patient and partner returned the baseline questionnaire. See flowchart for an overview (Fig. 1).

Data Outcome The outcome in the present study was “participation”, defined as whether or not the couple participated in the questionnaire

From the registers, we retrieved breast cancer-related variables for all patients, while all other variables were obtained for both patients and partners.

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Breast cancer-related variables Clinical information regarding the breast cancer was obtained from DBCG and included date of breast cancer surgery, prognostic and clinical variables, and treatment information for all eligible patients. DBCG was established in 1977 on a nationwide basis to ensure optimal treatment of operable breast cancer [14]. In 2012, 95 % of all breast cancer diagnoses in Denmark were included in DBCG. Older patients were slightly overrepresented among the 5 % not included in DBCG [15]. “Tumor size” was categorized into three groups: ≤20, 20 to 50, and >50 mm. “Affected lymph nodes” were categorized into three groups: 0, 1–3, and >3 affected lymph nodes. “Histological group” was categorized into three groups: ductal grade I, ductal grade II and III, and non-ductal. “Estrogen receptor status” was either positive or negative. Information on whether or not the patient had distant metastases was also included. “Type of surgery” was either mastectomy or lumpectomy. The variables “detected by public screening”, “allocated to radiotherapy”, “allocated to chemotherapy”, “allocated to endocrine therapy”, and “allocated to trastuzumab” were all dichotomous (yes/no). It was only possible to get information on the allocated treatment, rather than whether the patients had completed the treatment. “Time from surgery to study contact” was calculated as number of days from the date of surgery to the date on which the invitation was mailed. Socioeconomic variables Individual information on socioeconomic characteristics of patients and partners was obtained from the Integrated Database for Labour Market Research [16]. All socioeconomic variables referred to 2010, ensuring that the information related to the time when the couple decided on whether or not to participate in the study. The socioeconomic variables were defined with inspiration from CANULI, a Danish populationbased study on inequality, incidence of cancer, and survival from cancer [17]. “Level of education” was divided into three categories: Basic school included 7–12 years of primary, secondary, and/or grammar-school education; vocational education included persons educated from a technical or business college with a total of 10–12 years of education; and high education included ≥13 years of education. “Affiliation to the labour market” was divided into working, unemployed, retired and receiving disability pension. “Ethnicity” was divided into three groups: Danish ethnicity and immigrants or descendants from western or non-western countries, respectively. “Household disposable income” was calculated as (deflated household income)/(no. of persons in household0.6) [17], followed by division into quartiles; low income was defined as 1st quartile, middle as 2nd and 3rd quartile, and high as 4th quartile. “Number of children in the household” was

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categorized into: 0, 1, 2, and >2 children. We were able to calculate the length of cohabitation for the couples going 25 years back. Cohabitation was divided into 5-year intervals. By definition, “household disposable income”, “number of children in the household”, and “length of cohabitation” had the same value for patient and partner. Information on health-related factors From the Danish National Patient Register [18], we retrieved individual information on all hospitalizations since 1977, and since 1995 on both hospitalizations and outpatient visits. The register provides diagnostic codes according to ICD-8 and ICD-10. The codes were used to calculate Charlson Comorbidity Index as a measure of patient comorbidity and partner morbidity. The Charlson Comorbidity Index is a widely used to measure the comorbidity combining 19 different conditions. This weighted index score takes into account the number and the seriousness of the (co)morbid conditions [19, 20]. We calculated the index based on information prior to date of breast cancer surgery, i.e., the patient’s current breast cancer diagnosis was not included in the index. The Charlson Comorbidity Index score was divided into three categories: 0, 1, and ≥2. From the Danish National Prescription Register, we retrieved information on all individually dispensed prescriptions since 1995 [21]. To obtain an indicator of mental vulnerability, we defined two dichotomous (yes/no) variables “use of antidepressants within 12 months prior to surgery” and “use of antidepressants within five years prior to surgery”. Antidepressant prescriptions were identified as N06A according to the drug classification system ATC.

Analyzes The frequencies of the different prognostic and clinical variables for participating and non-participating patients were calculated. To analyze the associations between the breast cancer clinical variables and participation, logistic regression analyzes were used with participation as the dependent variable. The odds ratios (ORs) were adjusted for patient age at surgery and presented with 95 % confidence intervals (CI). The frequencies of the socioeconomic and health-related characteristics were calculated among participating and nonparticipating patients and partners. Associations between participation and each of the socioeconomic and health-related variables were calculated using logistic regression. The ORs for the patients were adjusted for patient age at time of surgery, and ORs for the partners were adjusted for partner age at time of surgery. “Household disposable income”, “number of children in the household”, and “length of cohabitation”, which

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had the same value for both patient and partner, were adjusted for the patient and partner age separately, and thus have two different age-adjusted ORs. The age-adjusted ORs are presented with 95 % confidence intervals. The self-reported reasons on the declination form for not participating were categorized into thematic categories based on the replies and were not predefined.

Ethics The study was approved by the Danish Data Protection Agency (ID: 2012-41-0901). The Regional Scientific Ethical Committee for Southern Denmark has assessed that the project falls outside the scope of projects to be notified to the Ethical Committee (ID: S-20110103). The study has the ClinicalTrials.gov Identifier: NCT01392066.

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not participating in the questionnaire study. For each patient, we extracted the main reason and defined 12 thematic categories (Fig. 1). The most frequent category was lack of energy covering statements like “have no energy to participate” and “prioritise to spend my/our energy on family, friends or other activities”. The second most frequent category was disapproval of the study or the questionnaires. This covered both the overall study subject and the nature of the questionnaire (length or content). Other illness of patient, partner or both was the third most frequent category. Couples who expressed that the breast cancer had very little impact on their lives, or who for other reasons felt that their breast cancer trajectory was not comparable to others, were grouped in a separate category labeled “disease history not relevant”. Generally, the amount of missing data was low and did not exceed 3 % for any variable besides “detected by public screening” with 10 % missing (Tables 1 and 2). Missing data were similarly distributed for participants and nonparticipants.

Results Of the 2254 eligible couples, 792 (35 %) completed the baseline questionnaires. The 2254 eligible patients had a mean age of 60 years (SD=11), partners had a mean age of 62 years (SD=12). The mean size of the tumor was 18 mm (SD=12), 84 % were estrogen receptor positive, and 39 % had axillary nodal invasion with a mean of 3.6 affected lymph nodes (SD= 4.8). Three patients had distant metastases and were all nonparticipants. A total of 26 % of the patients had a mastectomy, 48 % were allocated to chemotherapy, and 86 % to radiotherapy. The mean time from surgery to study contact was 60 days (SD=22). A total of 28 % of the couples had children living at home, on average 1.8 children (SD=0.03). After adjustment for patient age, participation was not statistically significantly associated with any of the breast cancer-related variables (Table 1). Several of the socioeconomic variables were associated with participation. Older age of patients as well as partners reduced participation. After adjustment for age, participation was reduced by low education, low income, receiving disability pension, or having non-western ethnicity. These associations were observed for both patients and partners. Having more than two children living at home increased participation, both after adjustment for patient age and partner age (Table 2). Of the health-related variables, reduced participation was found if partners had high morbidity, i.e., a score of 2 or more on the Charlson Comorbidity Index scale. The same tendency was observed for patients and for mild comorbidity, although not statistically significant. No associations were found with regard to the use of antidepressants (Table 2). Of the 1462 non-participating couples, 1062 declined to participate and 400 did not respond to the study invitation. Of the 1062 couples, 397 (37 %) stated one or more reasons for

Discussion Based on data from a couple-based longitudinal, nationwide study on psychosocial adjustment following breast cancer, this study showed that couple participation was associated with socioeconomic and health-related characteristics of both the patients and their partners. Low socioeconomic status and older age reduced participation. High morbidity in partners also reduced participation. No association between study participation and any breast cancer-related characteristic was observed. Further, it is notable that no association was found between participation and the use of antidepressants, reflecting mental vulnerability. This unique study has several strengths. It is based on a large, national sample, and data were available on all eligible couples, allowing an almost complete comparison of all participants and non-participants. Further, a nationwide clinical database, DBCG, was used to establish the cohort, making the inclusion independent of hospital staff. It is a limitation that some patients had to be excluded due to delay in registration to DBCG and delay due to practical reasons in the inclusion process. Thus, 762 patients did not meet the inclusion criterion of maximum of 4 months from surgery to study contact (Fig. 1). With regard to the generalizability of the study results, it is a limitation that the results are solely based on couples affected by breast cancer, i.e., one specific type of cancer, and only on female patients. The length and the intimate nature of the questionnaire may have influenced the willingness to participate. Intimate items and themes are a prerequisite for many couple-based psychosocial studies, and some length of the questionnaire is necessary to clarify

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Table 1 Breast cancer-related characteristics of 2254 Danish women newly diagnosed with primary breast cancer who were invited to a nationwide, couple-based study on psychological issues. Breast cancerParticipant, % (n) n=792 Tumor sizea ≤20 mm >20 mm and ≤50 mm >50 mm Affected lymph nodesb 0 1–3 >3 Histological groupc Ductal grade I Ductal grade II and III Non-ductal Estrogen receptor statusd Negative Positive Type of surgery Mastectomy Lumpectomy Detected by public screeninge No Yes Allocated to chemotherapy No Yes Allocated to radiotherapy No Yes Allocated to endocrine therapy No Yes Allocated to trastuzumab No Yes Time from surgery to contact 30 days or less 31–60 days 61–90 days 91–121 days Distant metastasesf

related characteristics association with study participation, for 792 participants and 1462 non-participants

Non-participant, % (n) n=1462

Odds ratio

Age adjusted OR (95 % CI)

71.3 (565) 25.9 (205) 2.3 (18)

70.7 (1034) 25.9 (379) 2.4 (35)

1 0.99 0.94

1 1.00 (0.82–1.22) 0.92 (0.51–1.65)

59.9 (474) 27.4 (217) 11.5 (90)

60.2 (880) 27.8 (406) 10.1 (144)

1 0.99 1.16

1 0.95 (0.78–1.17) 1.10 (0.82–1.46)

25.0 (195) 58.0 (452) 16.9 (132)

23.1 (333) 59.2 (852) 17.7 (255)

1 0.91 0.88

1 0.86 (0.70–1.07) 0.92 (0.70–1.22)

15.3 (120) 84.7 (666)

15.3 (222) 84.7 (1230)

1 1.00

1 1.08 (0.84–1.37)

25.4 (201) 74.6 (591)

26.9 (393) 73.1 (1069)

1 1.09

1 1.12 (0.91–1.36)

55.4 (399) 44.6 (321)

55.8 (731) 44.2 (580)

1 1.01

1 1.09 (0.90–1.31)

49.1 (389) 50.9 (403)

54.0 (789) 46.0 (673)

1 1.21

1 0.83 (0.67–1.03)

12.1 (96) 87.9 (696)

15.3 (224) 84.7 (1238)

1 1.31

1 1.16 (0.89–1.50)

27.7 (219) 72.4 (573)

26.5 (387) 73.5 (1075)

1 0.94

1 0.93 (0.76–1.13)

86.7 (687) 13.3 (105)

88.4 (1292) 11.6 (170)

1 1.16

1 1.09 (0.84–1.42)

4.6 (36) 54.4 (431) 26.3 (208) 14.8 (117)

3.7 (54) 57.6 (842) 27.8 (407) 10.9 (159)

1 0.77 0.77 1.10

1 0.73 (0.47–1.14) 0.74 (0.47–1.16) 1.07 (0.66–1.75)

No

792

1459

−

−

Yes

0

3

−

−

a

18 missing, b 43 missing, c 35 missing, d 3 missing, 13 unknown, e 223 missing, f no statistical analysis preformed due to the too small group with distant metastases

the relevant psychosocial issues. It is important to be aware that differences in study populations and the content and

nature of a given questionnaire may influence couples’ decision to participate.

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Table 2 Socioeconomic and health-related characteristics of 792 participating and 1462 non-participating couples affected by breast cancer and associations with study participation. The ORs for the patients are adjusted for the patient age at time of surgery, and ORs for the partners were adjusted

for partner age at time of surgery. “Household disposable income”, “number of children in the household”, and “length of cohabitation” have the same value for both patient and partner, are adjusted for the patient and partner age separately, and thus have two different age adjusted ORs

Patient

Partner

Participant % (n)

Nonparticipant % (n)

Odds ratio

79

1.1 (9)

5.5 (80)

0.15 (0.07–0.33)

–

3.0 (24)

8.9 (130)

0.23 (0.13–0.43)

–

Basic school

10.8 (85)

18.8 (270)

1

1

12.8 (100)

19.3 (274)

1

1

Vocational education

53.6 (420)

55.7 (799)

1.67

1.46 (1.11–1.93)

54.4 (425)

55.1 (783)

1.49

1.30 (1.00–1.70)

High education

35.6 (279)

25.5 (366)

2.42

1.98 (1.46–2.68)

32.9 (257)

25.6 (364)

1.93

1.67 (1.25–2.22)

62.3 (486)

49.0 (700)

1

1

63.9 (500)

51.4 (739)

1

1

2.3 (18)

2.8 (40)

0.65

0.64 (0.36–1.13)

2.7 (21)

2.7 (39)

0.80

0.79 (0.46–1.36)

Retirement

30.8 (240)

41.3 (590)

0.59

0.83 (0.64–1.09)

31.6 (247)

42.3 (608)

0.60

0.82 (0.64–1.05)

Disability pension

4.6 (36)

7.0 (100)

0.52

0.59 (0.39–0.88)

1.9 (15)

3.7 (53)

0.42

0.46 (0.25–0.82)

96.8 (765)

94.5 (1378)

1

1

97.1 (766)

94.0 (1371)

1

1

3.6 (52)

0.62

0.57 (0.33–0.99)

2.4 (19)

3.6 (52)

0.65

0.63 (0.37–1.08)

2.0 (29)

0.43

0.36 (0.15–0.82)

0.5 (4)

2.4 (35)

0.20

0.17 (0.06–0.49)

19.4 (153)

28.0 (408)

1

1

–

–

–

1

Middle (2nd–3rd 53.0 (418) quartile) Highest (4th 27.6 (218) quartile) Number of children in householde

48.4 (705)

1.58

1.40 (1.12–1.76)

–

–

–

1.39 (1.11–1.75)

23.6 (344)

1.69

1.49 (1.16–1.93)

–

–

–

1.48 (1.15–1.92)

Level of educationa

Affiliation to work marketb Working Unemployed

Ethnicityc Danish

Immigrants or 2.3 (18) descendants from western countries Immigrants or 0.9 (7) descendants from non-western countries Household disposable incomed Lowest (1st quartile)

0

66.3 (525)

75.3 (1101)

1

1

–

–

–

1

1

11.5 (91)

11.2 (163)

1.17

0.88 (0.64–1.20)

–

–

–

0.87 (0.64–1.19)

2

15.4 (122)

10.7 (156)

1.64

1.12 (0.81–1.54)

–

–

–

1.12 (0.81–1.54)

>2

6.8 (54)

2.9 (42)

2.70

1.79 (1.13–2.84)

–

–

–

1.84 (1.16–2.90)

≤5

9.1 (72)

6.8 (100)

1

1

–

–

–

1

6–10

8.1 (64)

6.0 (87)

1.02

0.99 (0.64–1.56)

–

–

–

0.98 (0.63–1.54)

Length of cohabitatione

11–15

8.0 (63)

7.9 (115)

0.76

0.74 (0.48–1.34)

–

–

–

0.76 (0.49–1.17)

16–20

8.5 (67)

8.6 (125)

0.74

0.73 (0.48–1.12)

–

–

–

0.74 (0.48–1.14)

>20

66.4 (526)

70.8 (1035)

0.71

0.90 (0.64–1.25)

–

–

–

0.92 (0.66–1.29)

Charlson comorbidity index 0

72.1 (571)

65.7 (961)

1

1

63.3 (501)

55.4 (810)

1

1

1

15.5 (123)

18.7 (274)

0.76

0.79 (0.62–1.00)

18.9 (150)

20.1 (294)

0.82

0.93 (0.74–1.17)

≥2

12.4 (98)

15.5 (227)

0.73

0.84 (0.64–1.09)

17.8 (141)

24.5 (358)

0.64

0.76 (0.60–0.96)

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Table 2 (continued) Patient Participant % (n)

Partner Nonparticipant % (n)

Odds ratio

Age adjusted OR (95 % CI)*

Participant % (n)

Nonparticipant % (n)

Odds ratio

Age adjusted OR (95 % CI)**

Use of antidepressants within 12 months prior to surgery No

89.3 (707)

88.0 (1287)

1

1

92.6 (733)

92.1 (1346)

1

1

Yes

10.7 (85)

12.0 (175)

0.88

0.89 (0.68–1.18)

7.5 (59)

7.9 (116)

0.93

0.99 (0.71–1.37)

Use of antidepressants within 5 years prior to surgery No

84.0 (665)

82.6 (1207)

1

1

86.7 (687)

87.4 (1278)

1

1

Yes

16.0 (127)

17.4 (255)

0.90

0.91 (0.72–1.15)

13.3 (105)

12.6 (184)

1.06

1.12 (0.87–1.45)

a

35 missing (patient), 51 missing (partner). b 44 missing (patient), 32 missing (partner). c 5 missing (patient), 7 missing (partner). d Same value for patient and partner, 8 missing. e Same value for patient and partner

*Adjusted for patient age at time of surgery. **Adjusted for partner age at time of surgery

To our knowledge, no other study has used clinical and administrative registers to study the participation in couplebased studies. However, two studies investigating participation in couple-based studies of breast cancer have been published, but these used other data sources and different recruitment processes [11, 12]. A study by Christie et al. [11] was based on a randomized controlled trial of 384 women with breast cancer. After the women had completed the baseline survey and intervention, partners were invited to participate in a separate study. Survey data on characteristics of the breast cancer women from the first part of the study were then used to investigate how various characteristics predicted the participation among the partners. In a study by Baider et al. [12], 292 women with breast cancer first agreed to participate in a survey, and subsequently the partners were asked to participate in a couple-based part of the study. Survey data on the patients were thus available for all invited couples and used to compare patients of participating partners with patients of non-participating partners. That study was performed longer after diagnosis than our study and was based on interviews rather than questionnaires. Baider’s and Christie’s studies are not directly comparable with ours. Both Baider et al. [12] and Christie et al. [11] used survey data from patients to compare patients of participating partners with patients of nonparticipating partners. It is a limitation of their approach that study participation was studied in a population defined by patient willingness to participate in a preceding part of the study. However, they had the advantage of having survey data available for the comparison of participants and non-participants. Christie et al. showed that partners were less likely to participate if patients reported to have low income or a feeling of lack of support from their partner, while having nonHispanic white ethnicity increased participation. Baider et al.

showed that partners were less likely to participate if patients reported low family support or more psychological distress, measured as higher intrusion and avoidance on the Impact of Event Scale [22]. Studies involving only patients affected by breast cancer and not their partners have found associations between participation and socioeconomic factors. Non-participants were shown to be older [23–28], have lower education [24, 26, 27, 29], lower income [28–30], belong to an ethnic minority [26], or have comorbidity [24, 28]. These findings are in line with what was found in our couple-based study. This may imply that socioeconomics influence participation in similar ways in single- and couple-based studies. In line with our results, none of these studies found participation associated with cancer-related variables, besides one. Lundh et al. [28] showed that when invited to a follow-up study 16 months after diagnosis, nonparticipants less frequently received radiotherapy, more were mastectomized, and had distant metastases and recurrent cancer. At the time of diagnosis, recurrence of cancer is not yet relevant and metastatic spread is seldom, thus it is not surprising that in our study, conducted shortly after diagnosis, we found different results. Our results add to the evidence that cancer-related characteristics have little or no impact on participation shortly after diagnosis, but may be a problem during follow-up or in studies conducted longer after diagnosis. To our knowledge, partner morbidity has not previously been studied with regard to participation in surveys. It is not surprising that complex morbidity of the partner is a burden for the couple, which can result in less energy to participate in this kind of research. We, therefore, suggest that future studies in both couple-based as well as patient and caregiver surveys and clinical trials are aware of the possible influence of partner morbidity and account for it, if possible.

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The finding of increased participation in couples with more than two children in the household was surprising. However, it is possible that these couples have to deal with particular family-related challenges in everyday life, which also may influence their relationship. They may feel an increased need to share their experiences or find it more relevant to participate in a couple-based study. Generally, in psychosocial research, addressing personal issues such as the couple relationship, emotional and sexual life, and self-selection processes may lead to an overrepresentation of couples who wish to share their personal information, whereas couples who experience difficulties in their relationship may be underrepresented. Participation was lower in couples from lower socioeconomic groups. Offering different ways to answer a questionnaire may increase participation from these groups. A study investigating the difference between participants answering a cancer survey online versus by telephone found that participants answering by telephone had lower income and education and were more likely to be non-Caucasian [31]. In our study, offering couples to answer by telephone was deselected, because it would have been too time-consuming and expensive. In conclusion, the results from this large, population-based study find that socioeconomic characteristics of patients and partners, and morbidity of partners may influence participation in couple-based psychosocial breast cancer research. Breast cancer-related characteristics do not seem to influence participation shortly after diagnosis. The results of this study underline the challenges in recruiting couples to research, especially couples with low socioeconomic status and may draw researchers’ attention to the possibility of participation bias in similar studies. It is likely that our results may be relevant in relation to other research areas as well, e.g., in studies on other cancer diagnoses or chronic illnesses. However, caution must be exerted when extrapolating the findings to different populations and different types of surveys. Acknowledgments The authors thank Camilla Tykgaard Clausen for her help with categorizing the free text from the declination forms returned by non-participants and Secretary Lise K. Stark for proofreading the manuscript. This study was funded by the Danish Cancer Society (Grant number R40-A1920-11-S2). The National Research Center for Cancer Rehabilitation, University of Southern Denmark, is funded by the Danish Cancer Society. The author(s) declared no potential conflicts of interests with respect to the authorship and/or publication of this article. Conflict interests statement The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. The authors have full control over all primary data and agree to allow the journal to review the data if requested.

References 1. Desantis C, Ma J, Bryan L, Jemal A (2014) Breast cancer statistics, 2013. CA Cancer J Clin 64:52–62. doi:10.3322/caac.21203

1915 2. Hagedoorn M, Sanderman R, Bolks HN, Tuinstra J, Coyne JC (2008) Distress in couples coping with cancer: a meta-analysis and critical review of role and gender effects. Psychol Bull 134:1–30. doi:10. 1037/0033-2909.134.1.1 3. Fergus KD, Gray RE (2009) Relationship vulnerabilities during breast cancer: Patient and partner perspectives. Psycho-Oncology 18:1311–1322. doi:10.1002/pon.1555 4. Hagedoorn M, Buunk BP, Kuijer RG, Wobbes T, Sanderman R (2000) Couples dealing with cancer: Role and gender differences regarding psychological distress and quality of life. PsychoOncology 9:232–242 5. Heins M, Schellevis F, Rijken M, Donker G, van der Hoek L, Korevaar J (2013) Partners of cancer patients consult their GPs significantly more often with both somatic and psychosocial problems. Scand J Prim Health Care 31:203–208. doi:10.3109/02813432. 2013.861153 6. Nakaya N, Saito-Nakaya K, Bidstrup PE, Dalton SO, Frederiksen K, Steding-Jessen M et al (2010) Increased risk of severe depression in male partners of women with breast cancer. Cancer 116:5527–5534. doi:10.1002/cncr.25534 7. Galea S, Tracy M (2007) Participation rates in epidemiologic studies. Ann Epidemiol 17:643–653 8. Dagan M, Hagedoorn M (2013) Response rates in studies of couples coping with cancer: a systematic review. Health Psychol. doi:10. 1037/hea0000013 9. Davern M (2013) Nonresponse rates are a problematic indicator of nonresponse bias in survey research. Health Serv Res 48:905–912. doi:10.1111/1475-6773.12070 10. Bolger N, Foster M, Vinokur AD, Ng R (1996) Close relationships and adjustment to a life crisis: the case of breast cancer. J Pers Soc Psychol 70:283–294 11. Christie K, Meyerowitz B, Stanton A, Rowland J, Ganz P (2013) Characteristics of breast cancer survivors that predict partners' participation in research. Ann Behav Med 03/01:1–7. doi:10.1007/s12160013-9477-7 12. Baider L, Andritsch E, Goldzweig G, Uziely B, Ever-Hadani P, Hofman G et al (2004) Changes in psychological distress of women with breast cancer in long-term remission and their husbands. Psychosomatics 45:58–68 13. Pedersen CB (2011) The Danish civil registration system. S c a n d i n a v i a n J P u b H e a l t h 3 9 : 2 2 – 2 5 . d o i : 1 0 . 11 7 7 / 1403494810387965 14. Moller S, Jensen MB, Ejlertsen B, Bjerre KD, Larsen M, Hansen HB et al (2008) The clinical database and the treatment guidelines of the Danish Breast Cancer Cooperative Group (DBCG); its 30-years experience and future promise. Acta Oncol 47:506–524. doi:10. 1080/02841860802059259 15. DBCG. Kvalitetsindikatorrapport for Brystkræft. Landsdækkende Klinisk Kvalitetsdatabase for Brystkræft: DBCG | Danish Breast Cancer Cooperative Group; 2012. Available from: http://www. dbcg.dk/PDF%20Filer/DBCG_rapport_2012.pdf. May 2014. 16. Thygesen LC, Daasnes C, Thaulow I, Brønnum-Hansen H (2011) Introduction to Danish (nationwide) registers on health and social issues: Structure, access, legislation, and archiving. Scandinavian J Pub Health 39:12–16 17. Dalton SO, Steding-Jessen M, Gislum M, Frederiksen K, Engholm G, Schuz J (2008) Social inequality and incidence of and survival from cancer in a population-based study in Denmark, 1994–2003: Background, aims, material and methods. Eur J Cancer 44:1938– 1949. doi:10.1016/j.ejca.2008.06.010 18. Lynge E, Sandegaard JL, Rebolj M (2011) The Danish national patient register. Scandinavian J Pub Health 39:30–33. doi:10.1177/ 1403494811401482 19. Charlson ME, Pompei P, Ales KL, MacKenzie CR (1987) A new method of classifying prognostic comorbidity in longitudinal studies: development and validation. J Chron Dis 40:373–383

1916 20. Sarfati D (2012) Review of methods used to measure comorbidity in cancer populations: no gold standard exists. J Clin Epidemiol 65: 924–933. doi:10.1016/j.jclinepi.2012.02.017 21. Kildemoes HW, Sorensen HT, Hallas J (2011) The Danish national prescription registry. Scandinavian J Pub Health 39:38–41. doi:10. 1177/1403494810394717 22. Horowitz M, Wilner N, Alvarez W (1979) Impact of event scale: a measure of subjective stress. Psychosom Med 41:209–218 23. Holm LV, Hansen DG, Johansen C, Vedsted P, Larsen PV, Kragstrup J et al (2012) Participation in cancer rehabilitation and unmet needs: a population-based cohort study. Support Care Cancer 20:2913–2924. doi:10.1007/s00520-012-1420-0 24. Christensen S, Zachariae R, Jensen AB, Vaeth M, Moller S, Ravnsbaek J et al (2009) Prevalence and risk of depressive symptoms 3–4 months post-surgery in a nationwide cohort study of Danish women treated for early stage breast-cancer. Breast Cancer Res Treat 113:339–355. doi:10.1007/s10549-008-9920-9 25. Pritzkuleit R, Waldmann A, Raspe H, Katalinic A (2008) The population-based oncological health care study OVIS— Recruitment of the patients and analysis of the non-participants. BMC Cancer 8:311. doi:10.1186/1471-2407-8-311 26. Sears SR, Stanton AL, Kwan L, Krupnick JL, Rowland JH, Meyerowitz BE et al (2003) Recruitment and retention challenges in breast cancer survivorship research: Results from a multisite,

Support Care Cancer (2015) 23:1907–1916

27.

28.

29.

30.

31.

randomized intervention trial in women with early stage breast cancer. Cancer Epidemiol Biomark Prev 12:1087–1090 Würtzen H, Dalton SO, Andersen KK, Elsass P, Flyger HL, Sumbundu A et al (2013) Who participates in a randomized trial of mindfulness-based stress reduction (MBSR) after breast cancer? A study of factors associated with enrollment among Danish breast cancer patients. Psycho-Oncology 22:1180–1185. doi:10.1002/pon. 3094 Lundh MH, Lampic C, Nordin K, Ahlgren J, Bergkvist L, Lambe M et al (2013) Changes in health-related quality of life by occupational status among women diagnosed with breast cancer-a population-based cohort study. Psycho-Oncology. doi: 10.1002/pon.3285 Geller BM, Mace J, Vacek P, Johnson A, Lamer C, Cranmer D (2011) Are cancer survivors willing to participate in research? J Community Health 36:772–778. doi:10.1007/s10900-011-9374-6 Boesen E, Boesen S, Christensen S, Johansen C (2007) Comparison of participants and non-participants in a randomized psychosocial intervention study among patients with malignant melanoma. Psychosomatics 48:510–516 Williams MS, Snyder DC, Sloane R, Levens J, Flynn KE, Dombeck CB et al (2013) A comparison of cancer survivors from the PROMIS study selecting telephone versus online questionnaires. PsychoOncology 22:2632–2635. doi:10.1002/pon.3330

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