These researchers assessed the effectiveness of a range of approaches used to recruit New Zealand adults (aged ≥18 years) to a large, fully automated smartphone-enabled nutrition intervention trial (no face-to-face visits were required) and to examine associations of recruitment strategies with participant demographics. Recruitment was through Internet and social media advertising, mainstream media advertising and research team networks. Recruitment of Māori and Pacific participants was a key focus and ethically relevant recruitment materials and approaches were used where possible. Over a 13-month period, there were 2448 registrations on the study website, and 1357 eligible individuals were randomised into the study. Facebook campaigns were the most successful recruitment strategy overall (43% of all randomised participants) and for all ethnic groups (Māori 44%, Pacific 44% and Other 43%). Recruitment strategy was significantly associated with age (p<0.001), household size (p<0.001), ethnicity (p<0.001), gender (p=0.005) and interest in healthy eating (p=0.022). Those recruited via Internet/social media were younger on average (31 years), whereas those recruited via radio and newspaper advertising were older (36.5 and 37 years, respectively). Facebook campaigns resulted in the highest absolute numbers of study registrations (n=966) and randomisations (n=584). Network strategies and Facebook campaigns cost least per randomised participant (NZ$4 and NZ$5, respectively) and radio advertising cost the most (NZ$179 per participant).
