This observational behavioural study examines whether individual differences in sleep quality, sleep timing, and chronotype are associated with prosocial allocation decisions in adults. Participants will complete self-report sleep and circadian questionnaires, including the Pittsburgh Sleep Quality Index and the Munich Chronotype Questionnaire, a 7-day sleep diary, and a brief computer-based Dictator Game allocation task.

The study does not involve sleep deprivation, sleep restriction, treatment, clinical diagnosis, medication, or medical devices. Participants will not be asked to change their sleep schedule. The Dictator Game decisions are hypothetical and do not affect participants' compensation. The study is intended to describe associations between naturally occurring sleep-related individual differences and behavioural allocation choices, not to diagnose or treat sleep or mental health conditions.

This is a non-clinical observational behavioural study of adults aged 18 years or above. The study investigates whether naturally occurring differences in subjective sleep quality, sleep timing, and circadian preference are associated with prosocial decision-making in a computer-based allocation task.

Participants will first provide informed consent and will be assigned a participant code so that research data can be pseudonymised. They will complete demographic questions and sleep-related self-report measures. These measures include the Pittsburgh Sleep Quality Index, which assesses subjective sleep quality over the previous month, and the Munich Chronotype Questionnaire, which assesses sleep timing on workdays and free days and provides chronotype-related variables. Participants will also complete a 7-day sleep diary recording daily sleep-related information such as bedtime, estimated sleep onset, wake time, rise time, naps, subjective sleep quality, and schedule-related information.

Prosocial allocation behaviour will be assessed using a brief computer-based Dictator Game task. In this task, participants make hypothetical allocation choices involving distributions of money between themselves and another party. No deception cover story will be used. Participants will not be falsely told that they are interacting with a real paired participant if no real allocation exists. Dictator Game choices are hypothetical and do not affect actual compensation.

The primary aim is to examine associations between sleep quality, sleep timing, chronotype-related measures, and prosocial allocation behaviour. Secondary analyses may explore whether 7-day sleep diary measures provide additional information beyond retrospective questionnaire measures. Exploratory analyses may examine whether chronotype, sleep timing, or time of day moderates associations between sleep-related measures and Dictator Game behaviour. These analyses will be interpreted cautiously and will not be used to make clinical claims.

The study is not designed to diagnose, treat, or induce any sleep disorder, mental health condition, or other clinical condition. The PSQI, MCTQ, and sleep diary are used as non-diagnostic research measures. No clinical diagnosis, treatment recommendation, or personalised sleep advice will be provided. The expected risks are minimal and may include mild boredom or tiredness, mild discomfort when reflecting on sleep habits or making self-other allocation decisions, minor inconvenience from completing the 7-day diary, and privacy concerns about sleep schedule information. Risk will be minimised through informed consent, voluntary participation, the right to withdraw, non-clinical wording, pseudonymisation, separate storage of identifiable records, and restricted access to research data.

Inclusion Criteria:

• Aged 18 years or above.
• Able to provide informed consent.
• Able to understand English or Chinese study materials.
• Able to complete computer-based behavioural tasks and self-report questionnaires.
• Willing to complete a 7-day sleep diary.

Exclusion Criteria:

• Aged under 18 years.
• Unable to provide informed consent.
• Unable to complete study materials in English or Chinese.
• Prior participation in the same study.
• Self-reported condition or circumstance that would make participation in a brief computer-based decision-making task or sleep-related questionnaires inappropriate or distressing.

Adults aged 18 years or above will be recruited as healthy volunteers from university and community settings. Eligible participants may include university students, university staff, and community adults who can understand English or Chinese study materials and complete computer-based behavioural tasks, sleep-related questionnaires, and a 7-day sleep diary. The study is not limited to PolyU students and is not designed to recruit participants with any specific sleep disorder, mental health condition, or clinical diagnosis.

Individual participant data will not be shared outside the approved research team. Study findings will be reported in aggregate form only. Pseudonymised or anonymised data may be retained for future ethically approved research only if permitted by participant consent and institutional ethics approval.