Control group participants received neutral, informational content about lung cancer and screening. This content included lung cancer's status as a leading cause of cancer mortality, the challenges of late-stage diagnosis, and LDCT as the gold standard screening method. Participants were informed that high-risk individuals, particularly long-term smokers, require annual screening due to elevated cancer risk, with each participant explicitly told they qualified as high-risk due to their smoking history. Meanwhile, CanSPUC and its purpose were also shown to the participants. The screening participation question for controls was framed as: "We provide available time slots for free lung cancer screening. You can directly view available appointment times and make reservations according to your preference. Would you like to schedule lung cancer screening?"

Intervention participants received the same neutral information plus a default option nudge. The critical modification involved reframing the screening participation measure as: "We have already scheduled a free lung cancer screening appointment for you, which you can attend at your convenience. If you do not wish to participate, please indicate below." We also default to "Yes, I would like to make an appointment for lung cancer screening and see the available hours for lung cancer screening" for this question.

Control group participants received neutral, informational content about gastric cancer and screening. This content included gastric cancer's status as a cause of cancer mortality, the challenges of late-stage diagnosis, and endoscope as the gold standard screening method. Participants were informed that high-risk individuals require screening per 5 years, with each participant explicitly told they qualified as high-risk due to their living regions. Meanwhile, CanSPUC and its purpose were also shown to the participants. The screening participation question for controls was framed as: "We provide available time slots for free gastric cancer screening. You can directly view available appointment times and make reservations according to your preference. Would you like to schedule gastric cancer screening?"

Participants in this arm are subjected to a behavioral "nudge" using a default option mechanism during a simulated online appointment process for cancer screening. Instead of being asked to actively schedule an appointment (an opt-in approach), the screening appointment is presented to them as pre-selected or pre-scheduled (an opt-out approach). Furthermore, to evaluate the ethical and behavioral impact of transparency, this intervention uniquely includes a "disclosure" phase: after the initial decision, participants are explicitly informed about the nudge strategy that was just applied to them, and their screening intention is immediately re-measured.

This outcome is assessed via a dichotomous choice (Yes/No) embedded in the simulated online scheduling system within the questionnaire. The value reported will be the percentage of participants who choose to accept and schedule the screening appointment.

This measure is assessed via a self-reported questionnaire using a Likert scale. Scores range from 1 to 5, where 1 indicates a very negative attitude and 5 indicates a very positive attitude. Higher scores represent a better attitude towards the nudge strategy.