This single-blinded randomized controlled trial with cost-minimization analysis was conducted as part of a naturalistic observational study on Chinese primary care patients with lower urinary tract symptoms (LUTS) . There were two sampling frames for the study.
Sample A (Continence care clinic)
All new patients referred for services at a nurse-led continence care clinic at one of four government-funded General Out-Patient clinics (GOPC) across Hong Kong were identified from the appointment list and screened for LUTS. All eligible subjects were invited to participate in the study.
Sample B (GOPC waiting room)
Waiting room patients waiting to consult a doctor at one of another four GOPC locations were consecutively screened for LUTS. All eligible subjects were invited to participate in the study.
For both sampling frames, a modified International Consultation on Incontinence Questionnaire-Urinary Incontinence-Short Form (ICIQ-UI SF) questionnaire was used to screen for patient eligibility . Patients with scores ≥ 3 were considered to have LUTS. Patients were excluded if they were aged < 18 years, could not understand Cantonese, refused to participate, or were too ill to give consent.
Eligible patients were identified and consecutively approached by trained field workers to invite them to take part in the longitudinal telephone survey. The aims, procedures and nature of the naturalistic observation study were explained. Patients were also informed about the timing of incentive payments (either up-front or delayed incentive payment), according to the randomization list. Subjects were blinded to the alternate payment method. In other words, patients who were assigned to receive up-front an incentive payment did not know there was a delayed incentive payment group and vice versa. Subjects who consented were asked to provide their contact details for telephone surveys that were administered by blinded interviewers who were not aware of the incentive payment method allocation.
All patients were informed at the time of consent that both interviews (baseline and follow-up) would take approximately 15 min to complete.
Subjects were assigned to either the up-front incentive payment group or delayed incentive payment group by simple randomization on a 1:1 basis with random numbers generated by a computer. A statistician who was not involved in subject recruitment or patient interviews undertook the randomization.
The incentive payment was in the form of a supermarket gift voucher to the value of HD$50 (US$6.50) and could be used in lieu of cash at a major supermarket chain.
Up-front payment group
Each subject was handed a supermarket gift voucher valued at HKD$ 50 (US$6.50) at time of recruitment immediately following consent to participate. They were required to sign a receipt confirming they had received the voucher. There was no extra administrative work for the incentive payment afterwards.
Delayed payment group
We collected the mailing address of each subject at the time of enrollment. Each subject was posted a supermarket gift voucher valued at HKD$50 (US$6.50) with a self-addressed envelope for the return of a signed receipt slip. This was sent after the completion of their 1-year follow-up telephone interview. Prior to posting the gift vouchers, each subject was phoned to confirm the address and reminded to return a signed receipt by post to confirm that they had received payment.
Subjects were interviewed by telephone two weeks after recruitment (baseline) and again at 1-year after the baseline interview by trained interviewers who were blinded to the randomization. Trained interviewers administered all surveys with a computer-aided telephone interviewing system between 10:00 am and 10:30 pm on weekdays. A maximum of five attempts were made for unanswered calls. Subjects answered a structured questionnaire on the severity of LUTS, health-related quality of life, mental health, service utilization, co-morbidities and socio-demographics. There were 77 items in the baseline interview and 51 items in the 1-year follow-up interview.
Primary outcome: baseline and 1-year follow-up telephone survey response rates.
Secondary outcome: the cost per subject who had completed both baseline and 1-year surveys.
Baseline socio-demographic and clinical characteristics between both groups were compared by chi-square test for categorical variables, and by independent t-test for continuous variables. Chi-square test was used to compare the consent and response rates at baseline and 1-year follow-up telephone surveys between groups. The cost minimization analysis included all relevant direct costs including the cost of the supermarket voucher, staff costs for the manpower administering the baseline and 1-year telephone interviews, staff costs for the administrative work related to the mail out of the incentive payments as well as the cost of consumables such as postage and stationery. The cost per completed survey at 1-year for both groups was calculated.
A meta-analysis study on mail survey response rates found an overall response rate of 53.0 % for up-front incentive payment and 41.1 % for delayed incentive payments . Using this, to achieve 90 % power to detect a difference between the group proportions by Chi-square test with a 0.05 significance level, an estimated sample size of 360 subjects was needed in each group.
The study protocol of the present study was approved by the institutional review boards: the University of Hong Kong/Hospital Authority Hong Kong West Cluster, Hong Kong East Cluster Kowloon West Cluster, and Kowloon East Cluster. Written informed consent for participation in the study was obtained from participants.