How to effectively design public health interventions: Implications from the interaction effects between socioeconomic status and health locus of control beliefs on healthy dietary behaviours among US adults.

This study investigated whether individuals with different socioeconomic status (SES) should be provided differently tailored health messages to promote healthy dietary behaviour (HDB). Prior research has suggested that people with different SESs tend to exhibit different types of beliefs about health, but it remains unclear how SES interacts with these beliefs to influence health outcomes. To better understand the differences in HDB between high- and low-SES populations and propose effective intervention strategies, we examined (i) how SES is associated with HDB, (ii) how internal health locus of control (HLC) and powerful others HLC are associated with HDB, and (iii) how SES interacts with internal and powerful others HLC to influence HDB. Using data from the Annenberg National Health Communication Survey, collected from 2005 to 2012 (N = 6,262) in the United States, hierarchical multiple regression analyses were conducted. Education level was found to be positively associated with HDB, while income level was not. Both internal and powerful others HLC beliefs were positively associated with HDB. The positive relationship between internal HLC and HDB strengthened as the level of education and income increased, whereas the positive relationship between powerful others HLC and HDB weakened as respondents' education level increased. These results suggest that the design and delivery of communication messages should be tailored to populations' specific SES and HLC beliefs for effective public health interventions. For example, messages enhancing internal HLC (e.g. providing specific skills and knowledge about health behaviours) might be more helpful for the richer and more-educated, while messages appealing to one's powerful others HLC beliefs (e.g. advice on health lifestyles given by well-known health professionals) might be more effective for less-educated people.