Does change in intergenerational contact alter adult loneliness and ikigai? A within-person fixed-effects analysis of a four-wave national panel in Japan

Purpose. This project examines whether everyday contact between adults and the child/youth generations (ages 0–19) affects adults' own well-being — specifically loneliness and ikigai (sense of life worth living) — in Japan, a society undergoing rapid population aging and declining birth rates. Age segregation in daily life has long been identified as a structural root of intergenerational disconnection (Hagestad & Uhlenberg, 2005; Uhlenberg & De Jong Gierveld, 2004), and the WHO Commission on Social Connection (2025) has recently elevated social disconnection to a global public-health priority. However, nationally representative longitudinal evidence on whether within-person change in intergenerational contact translates into change in adult well-being remains scarce. Data and design. The confirmatory study uses four annual waves (2022–2025) of JACSIS (Japan COVID-19 and Society Internet Survey), a nationwide internet survey, linked at the individual level (four-wave complete panel N = 13,360). The primary analysis is a two-way (individual + wave) fixed-effects regression of loneliness (3-item UCLA scale) and ikigai (0–10) on the frequency of contact with the 0–19 age bands, with time-varying covariates, cluster-robust standard errors, and pre-specified sensitivity and robustness analyses (three-wave panel, first differences, attrition weighting, fixed-effects ordered logit, reverse-lag models, E-values, and a contrast exposure). Preregistration and open science. Because the authors already hold the data, this preregistration follows the template for secondary data analysis (van den Akker et al., 2021), with full disclosure of all prior data access. No bivariate association between the exposure and any outcome has been computed. The analysis pipeline is developed and frozen on blinded data (outcome columns shuffled within waves) and will be run on the real data exactly once after this registration is made public. Hypotheses are evaluated against a smallest effect size of interest (standardized β = 0.03), with all deviations to be reported transparently (Nosek et al., 2018). Expected outcomes. The project will deliver (i) confirmatory estimates of the within-person association between intergenerational contact and adult loneliness/ikigai, including dose–response and gain/loss symmetry; (ii) a separate descriptive report of national estimates and 2022–2025 trends in intergenerational contact; and (iii) related studies on non-kin positive childhood experiences and on parent–child dyads, each governed by its own frozen specification. Results are intended to inform policies on social connection and intergenerational integration regardless of the direction of findings. References Hagestad, G. O., & Uhlenberg, P. (2005). The social separation of old and young: A root of ageism. Journal of Social Issues, 61(2), 343–360. https://doi.org/10.1111/j.1540-4560.2005.00409.x Nosek, B. A., Ebersole, C. R., DeHaven, A. C., & Mellor, D. T. (2018). The preregistration revolution. Proceedings of the National Academy of Sciences, 115(11), 2600–2606. https://doi.org/10.1073/pnas.1708274114 Uhlenberg, P., & De Jong Gierveld, J. (2004). Age-segregation in later life: An examination of personal networks. Ageing & Society, 24(1), 5–28. https://doi.org/10.1017/S0144686X0300151X van den Akker, O. R., Weston, S., Campbell, L., Chopik, W., Damian, R., Davis-Kean, P., Hall, A., Kosie, J., Kruse, E., Olsen, J., Ritchie, S., Valentine, K. D., van 't Veer, A., & Bakker, M. (2021). Preregistration of secondary data analysis: A template and tutorial. Meta-Psychology, 5, Article 2625. https://doi.org/10.15626/MP.2020.2625 World Health Organization. (2025). From loneliness to social connection: Charting a path to healthier societies (Report of the WHO Commission on Social Connection). https://www.who.int/publications/i/item/978240112360