Sample size and feasibility

The sample size calculation was based on the proposed multivariable analysis that examines factors influencing the frequency and the perceived effectiveness of self-management behaviours. The initial sample size calculation estimated that 130 participants would be required (degree of freedom of independent variables x 10) to remain in the study at time 3 (Table 4.3)²⁹⁴. This estimation was directed by Tabachnick and Fidell (2012) in the absence of knowledge of pilot data in the area²⁹⁴. While it was not possible to accurately predict the attrition rate based on local data, a recent Australian longitudinal study of 163 patients with advanced cancer successfully retained 75% of the participants at week 12²⁷⁰. The attrition rate for this study was thus predicted to be approximately 25% at week 12. This population included 31% of patients with regional or local metastases and 69% of patients with

Chapter 4: Methods 77

distant metastases. With this data in mind, this study took a more conservative estimation of an attrition rate of 35% at 8 weeks (time 3 of the present study).

Table 4.3. Sample size calculation

Degree of freedom required

Supposed sample size by time 3 (n)

Estimated attrition rate by time 3

Number of patients required at baseline (n)

13 130 35% 200

In terms of the feasibility of recruitment, the estimated number of patients with advanced cancer with fatigue severity of greater than three out of ten on a numeric analogue scale and the estimated response rate was considered. In 2005, Bradley and her research team reported that 69% of patients with advanced cancer receiving radiotherapy (n=1296) experienced fatigue with a severity of 3/10 or above on a numeric analogue scale²⁹⁵. In 2009, another cross-sectional study investigating the patterns of fatigue in a population of patients with advanced cancer achieved a response rate of 65%²⁹⁶. With reference to the data discussed above, the researcher estimated that 446 patients would need to be approached (Table 4.4).

During the design of the study, no local system existed that collected information on the total number of patients with advanced cancer treated by the CCS at the RBWH. The most relevant statistics in relation to patients with advanced cancer were the number of patients with cancer referred to the Specialist Palliative Care Service and the number of patients with cancer receiving radiotherapy with palliative intent. According to the local registry (HBCIS), the Specialist Palliative Care Service at the RBWH received 570 referrals of patients with advanced cancer in Year 2009²⁹⁷. According to the local registry of the Queensland Radium Institute (powered by Mirrabooka Systems), the total number of patients with metastatic cancer who received palliative radiotherapy at the RBWH was 606 in Year 2007 ²⁹⁸. These numbers did not include all patients with advanced cancer treated by the CCS at the RBWH. Although these statistics were not specific to the targeted primary tumour groups in this study, these statistics indicated that it would be possible to approach 446 patients over a period of less than 12 months.

Table 4.4. Feasibility calculation

Number of patient required at baseline (n)

Percentage of patients with fatigue severity

over 3/10 on a NRS

Estimated response rate

Number of eligible patients required to

approach

200 69% 65% 446

Strategies to reduce attrition

All reasons for attrition were recorded for this study. All available data were analysed and any potential bias due to attrition and drop outs are reconciled in Chapter Seven of this dissertation. While some reasons for attrition, such as death, could not be prevented, a range of strategies were employed to improve compliance and reduce attrition in research involving vulnerable populations²⁹⁹. Strategies such as allowing flexibility in scheduling the telephone follow-up interviews, having a second contact number for the participants/caregivers, conducting the research in a comfortable environment for participants and demonstrating a non-judgmental attitude were employed in this study³⁰⁰. Given that the research process with vulnerable populations is complex, stressful and time consuming for the researcher, the researcher had to prepare for foreseeable issues during data collection³⁰¹. The researcher had six years of previous clinical experience in the capacity of an advanced practice nurse, providing palliative care and consultations in both inpatient and outpatient settings. Therefore, the researcher was prepared to optimise retention rates during both face-to-face and telephone interviews.

4.6.5 Sampling strategy and procedures

The investigator provided in-service education sessions to explain the study to the medical staff, nurses and other health professionals of the CCS at the RBWH.

Information was also made available in written form and distributed to all professionals working in the CCS. The researcher visited the work areas in CCS daily (Department of Radiation Therapy, Outpatient Day Therapy Unit, Outpatient Clinics and Oncology Inpatient Unit) to facilitate the referral process. Eligible patients were approached by a clinician and were asked for agreement for their information to be passed to the researcher. Upon agreement, the clinician then

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referred the patient to the researcher for the consent process. The recruitment procedures for this part of the study were the same as those for the semi-structured interviews as described in Section 4.3.5. After patient consent was obtained, baseline data were collected and the patients were also asked what time would best suit them for telephone follow-up interviews to occur. Patients were assured that the time for the interview would remain flexible, but would be as close as possible to 4 and 8 weeks from the initial interview. Dates for all interviews were recorded.

For this stage of the study, two researchers (the doctoral candidate and a research assistant) were involved in data collection. The research assistant was a cancer care nurse with clinical experience in caring for patients with advanced cancer. She held a Graduate Certificate of Cancer Nursing, and was provided with training and a standard script to ensure consistency throughout all telephone interviews. No inter-rater reliability analysis was conducted as no duplicate interviews or assessments were conducted by both data collectors. Duplicate interviews were avoided as it would further increase the burden on the participants.