Population aging has drawn the attention of policymakers toward public health and productivity issues.1 The United Nations’ Sustainable Development Goal #3 calls to “ensure healthy lives and promote well-being for all at all ages”, and #8 calls to “promote sustained, inclusive and sustainable economic growth, full and productive employment and decent work for all”.2 These goals aim to prepare society for the challenges associated with population aging and to support and provide older adults with opportunities to continue to contribute to society. Older adults can contribute productively to society in many ways, such as through volunteer work. Engaging in volunteer work can be beneficial for older adults themselves and at societal and political levels3; it mitigates the effects of retirement and enables older adults to live fulfilling lives through social participation. Furthermore, volunteer work helps older adults develop proactive and effective self-management skills, erase the negative image of them being “useless oldsters”, and achieve successful and active ageing.4 In the White Paper on the Aging Society, the Ministry of Health and Welfare in Taiwan outlined several approaches for encouraging older adults to participate in society, erasing stereotypical impressions, and reducing age discrimination. Approaches included promoting volunteer work, providing relevant training, and encouraging institutions and organizations to provide volunteering opportunities for older adults.5

Volunteer work is a measure of the productivity of older adults in that it enables older adults to continue contributing to society. In Taiwan, volunteer work participation rates are 63.1 % among individuals aged 65-74 years and 30.9 % among individuals aged ≥ 65 years.6 Most older adults participating in volunteer work in Taiwan provide preventive care at community-based facilities, such as community care centers, which involves performing home visitations, greeting calls, meal deliveries, service referrals, and participating in health promotional activities.7 Preventive care performed by older volunteers benefits not only those on the receiving end but also the older volunteers themselves, because engaging in preventive care enhances one's understanding and awareness of aging, thereby serving to prepare older volunteers for their expected future experiences.

Studies on volunteering have mostly focused on motivation and attitude toward rendering help to others.8, 9, 10, 11 Few studies have investigated volunteer competency or volunteer work requirements, particularly among older volunteers and volunteer work typically performed by older adults. Assessing the competency of older volunteers and providing them with adequate training before they start working can ensure that they quickly adapt to their tasks. The older volunteer competency scale (OVCS) was developed by our research group based on the results of a literature review, focus group interviews, and the Delphi method. The OVCS consists of 35 items across three dimensions: service awareness, service skills, and teamwork. Although the scale exhibits favorable expert validity in content importance, content adequacy, and descriptive clarity, the psychometric properties of the scale are unknown. Thus, this study aimed to investigate the factorial structure, test-retest reliability, and internal consistency of the OVCS and establish its reliability and validity by using a large sample.