This thesis comprises three main parts, each using single dataset. The first part involves two population-based surveys using data from the Tobacco Control Policy-related Survey. The second part is a secondary analysis of the 'Quit-to-Win' smoke-free campaign. The third part is a randomized clinical trial on smoking cessation for hospitalized patients who smoke (HKU Project code: 17614621). All data will be securely stored on the permission-protected team drive.