The study aims:

1. To test the effect of providing social comparison information on increasing physical activity among Singaporean adolescents.
2. To test whether providing social comparison information increases physical activity more when it is provided publicly compared to when it is provided anonymously.

Childhood and adolescent obesity represents a major public health challenge worldwide. Singapore is no exception as the prevalence of obesity among children was estimated at 12%. Overweight and obese children are more likely to become obese adults, to develop non-communicable diseases at a younger age, and to have a shorter life expectancy. One of the main reasons behind the growing obesity epidemic is low levels of physical activity. Previous literature shows evidence of a steep decline in physical activity among boys after the primary school years and low levels of activity among girls throughout the primary and high school years in Singapore. Daily step counts are found to be up to 35% short of the recommended daily steps for adolescents. Low levels of physical activity are also associated with lower psychological well-being among adolescents. Thus, it is important that interventions aimed at increasing physical activity target adolescent years.

In this study, the investigators propose to test the effectiveness of providing social comparison information on increasing physical activity among adolescents. Participating adolescents will be randomized into a group and groups will be randomized into one of two study arms in a 4-month walking program:

Private arm: At the end of each week, participants will be provided with the number of steps logged by the participants in their group. The number of steps will be ranked from highest to the lowest without any identifiable information about the participants.

Public arm: At the end of each week, participants in this arm will be provided with the same information as in the other arm plus the names of the participants corresponding to the number of steps logged.

Social comparison information will be provided to the study participants via SMS. We will conduct a 4-month two-arm RCT to test whether social comparison information increases physical activity more when it is disclosed publicly compared to when it is provided anonymously. The primary outcome is the average number of steps taken per week by participants. Study outcomes relating to physical activity and health-related quality of life for participants will be evaluated at baseline and 4 months. Step activity will be tracked in real time via Fitbit wireless pedometers throughout the study.

Inclusion Criteria:

• The study's target population is adolescents aged 13-16 years. Participants should be Singaporean citizens or permanent residents. Participants should be English-speaking. Participants should be willing to wear a pedometer for 4 months. Only participants who provide at least 8 (out of 14 days) valid days of pedometer data including at least 2 days of the weekend at baseline will be included.

Exclusion Criteria:

• Participants will be asked to complete a short screener questionnaire to ensure that they are healthy enough to participate. Participants reporting the following will be excluded:
• Having any medical condition that may limit their ability to walk as a means of physical activity
• Are unwilling to wear a wireless pedometer for 4 months

Participants will also be screened with a Physical Activity Readiness Questionnaire (PAR-Q). Those who answer 'YES' to any PAR-Q question will be permitted to enroll only if they provide written approval from a medical doctor.

Upon request from the principal investigator, individual participant data will be available to other researchers for secondary analysis purposes, such as meta-analyses, reanalysis or replication of results. Any data that will be shared will be de-identified so privacy of the participants will be protected.