The effect of timing of incentive payments on response rates for cohort study telephone interviews in primary care setting with cost-minimization analysis, a randomized controlled trial

Table 3 Cost per subject who completed baseline and follow-up interviews

		Up-front payment		Delayed payment
Resource component	Unit cost (USD)	n	n X unit cost (USD)	n	n X unit cost (USD)
Incentive
Coupon	6.50	360	2340	205	1332.50
Staff
Baseline interview^a	2.18	259	565.66	260	567.84
12-month interview	2.18	201	438.98	205	447.72
Administrative work for payment at 12-month^b	1.82	0	0.00	205	373.10
Stationary
Letter to patient at 12-month	0.01	0	0.00	205	1.68
Postage	0.44	0	0.00	205	90.61
Two envelopes	0.12	0	0.00	205	25.05
Total cost (USD)			3344.64		2838.50
Number of subjects successfully contacted at 12 months			201		205
Cost (USD)/successful subject at 12 months			16.64		13.85

^aCalculation was based on 12 mins/subject to process each incentive payment and an administrative staff cost of 10.9 USD
^bCalculation was based on 10 mins/subject to process each incentive payment and an administrative staff cost of 10.9 USD

ISSN: 1471-2288