If we want to 'do the most good' then two fundamental - but often overlooked - questions are 'What is good?' and 'How do we measure it'? Cost-effectiveness - both inside and outside effective altruism - is assessed in terms of health, wealth, intuitive judgements, or some mix of three. In this talk, Michael will explain why a simpler, better alternative is 'subjective wellbeing', using self-reports of happiness and life satisfaction, and share the latest research from the Happier Lives Institute showing how this could and should radically alter our ideas about how to do the most good, perhaps changing our focus from alleviating poverty to treating mental health. This talk aims to introduce people to some of the ideas underlying cause prioritisation and is most relevant for those interested in global health and wellbeing. Effective Altruism is a social movement dedicated to finding ways to do the most good possible, whether through charitable donations, career choices, or volunteer projects. EA Global conferences are gatherings for EAs to meet. You can also listen to this talk along with its accompanying video on YouTube.