a1 Clinical Trials Research Unit, School of Population Health, University of Auckland, Private Bag 92019, Auckland, New Zealand
a2 Department of Public Health, Wellington School of Medicine & Health Sciences, University of Otago, New Zealand
Objective To pilot the design and methodology for a large randomised controlled trial (RCT) of two interventions to promote healthier food purchasing: culturally appropriate nutrition education and price discounts.
Design A 12-week, single-blind, pilot RCT. Effects on food purchases were measured using individualised electronic shopping data (‘Shop ’N Go’ system). Partial data were also collected on food expenditure at other (non-supermarket) retail outlets.
Setting A supermarket in Wellington, New Zealand.
Participants Eligible customers were those who were the main household shoppers, shopped mainly at the participating store, and were registered to use the Shop ’N Go system. Ninety-seven supermarket customers (72% women; age 40 ± 9.6 years, mean ± standard deviation) were randomised to one of four intervention groups: price discounts, nutrition education, a combination of price discounts and nutrition education, or control (no intervention).
Results There was a 98% follow-up rate of participants, with 85% of all reported supermarket purchases being captured via the electronic data collection system. The pilot did, however, demonstrate difficulty recruiting Maori, Pacific and low-income shoppers using the electronic register and mail-out.
Conclusions This pilot study showed that electronic sales data capture is a viable way to measure effects of study interventions on food purchases in supermarkets, and points to the feasibility of conducting a large-scale RCT to evaluate the effectiveness of price discounts and nutrition education. Recruitment strategies will, however, need to be modified for the main trial in order to ensure inclusion of all ethnic and socio-economic groups.
(Received December 14 2005)
(Accepted May 24 2006)
(Online publication March 05 2007)