Sawyer, K., Hanafi, A., Freeman, T., Burke, C., Adams, S., Aveyard, P., Jacobsen, P., Taylor, G., 2025. Dataset for "What is the effect of presenting evidence of the mental vs physical health benefits of quitting smoking on motivation to stop smoking? An online randomised controlled experiment". Bath: University of Bath Research Data Archive. Available from: https://doi.org/10.15125/BATH-01424.