A Causal Analysis of Five Population-Wide Health Interventions: Evidence From New Zealand Panel Data

In the health sciences, robust causal inference methods have been developed to provide evidence of causality particularly in contexts in which conducting randomised experiments are impractical. These methods are rarely employed in psychological research. This thesis employs causal methods to investigate the effects of five macro-level public health interventions on outcomes in prejudice and human flourishing — areas that are of considerable interest to both psychological inquiry and public health. Utilising national panel data from the New Zealand Attitudes and Values Study, I adapt VanderWeele’s (2017a) multidimensional model of human flourishing into five domains: reflective well-being, health, social well-being, self-directed well-being, and embodied well-being. Prejudice is operationalised through feeling thermometers measuring warmth toward social groups. In a series of five studies, I employ a natural experiment (Study 1) and modified treatment policies (Studies 2-5) to address causal 'what-if' questions, estimating the impact of these interventions (exposures) on their outcomes.

Study 1 uses the COVID-19 pandemic and its associated lockdowns that occurred during 2020 in New Zealand as a natural experiment to infer population-wide changes in prejudicial attitudes. The results indicated reduced warmth toward Chinese, Asians (broadly defined), immigrants, Muslims, refugees, Indians, and the mentally ill. Notably, changes in warmth were not detected toward NZ Europeans, Māori, Pacific Islanders, the overweight, or the elderly. Overall, these findings suggest that in New Zealand, pandemic prejudice may spread beyond minority groups associated with the virus to other groups perceived as non-prototypical of national identity. In the context of this thesis, these findings demonstrate causal methods can be applied to panel data through a natural experiment design to investigate questions of psychological interest that would otherwise be unfeasible for experimentation. In Study 2, I shift focus to using the modified treatment policy design to study the effects of subjective empowerment on multidimensional flourishing. Using three waves of panel data, I compare the population’s outcomes under two exposure conditions: (1) the ‘null’ exposure, which is simply their actual level of subjective empowerment; (2) the subjective empowerment intervention, in which everyone’s level of subjective empowerment is increased by 1-point (on a 7-point Likert scale), capped at 7. By contrasting the effects of these interventions, I find that subjective empowerment causes wide-spread benefits on outcomes across the five measured dimensions of human flourishing, including enhanced subjective health, greater self-esteem, and reduced depression. These findings validate previous experimental results with real-world evidence and offer a road map for investigating causal questions of basic psychological interest.

In Study 3, using a similar methodology to Study 2, I investigate how social belonging influences human flourishing outcomes. I contrast the expected outcomes under two different interventions: (1) a social belonging intervention, in which the population increases their level of social belonging by 1 point (on a 7-point Likert scale), and (2) the ‘null’ exposure, which is merely the population’s observed levels of social belonging. The findings reveal that social belonging positively affects multiple outcomes of flourishing, including more gratitude, meaning in life, self-esteem, and reduced vengefulness. These results build on previous experimental findings by providing causal evidence of the impact of 'real-world' social belonging on outcomes in human flourishing. Importantly, the effect sizes for improved subjective health, self-esteem, and meaning in life are smaller than those found in experimental literature.

In Study 4, I evaluate the effects of exercise on human flourishing. Comparing the outcomes of increasing weekly exercise by 1 standard deviation (about 1 hour/day) to no exercise, the results indicate that exercise increases relationship satisfaction, gratitude, life satisfaction, and reduces depression; however, it also increases fatigue, reduces sense of neighbourhood community, and lowers sexual satisfaction. This study contributes to our understanding of the validity of observational causal methods by benchmarking results against experimental findings and provides causal evidence in areas less explored in the experimental literature.

In Study 5, I evaluate the effects of spiritual identification on multidimensional flourishing. By simulating interventions that either enhance or diminish spiritual identification, I find that increased identification positively influences sense of meaning and purpose in life, gratitude, and self-esteem. Interestingly, spiritual identification also appears to increase anxiety and future insecurity. Because spiritual identification is challenging to study in experimental settings, these findings provide valuable causal evidence for social psychological theories on the role of spiritual identification in promoting human flourishing.

In the discussion, I explore future directions for empirical research and potential applications for the findings from this thesis. The results from Studies 2-5 show evidence of benefits in human flourishing for the general population, but certain populations may respond more strongly to the modelled interventions. Future research may be interested in discerning whether effects are more pronounced within specific subgroups. Secondly, researchers may examine whether certain variables mediate causal relationships between exposures and outcomes. Finally, recommendations are offered for policymakers interested in using the insights from this thesis to guide decisions on promoting human flourishing.