In epidemiological or clinical studies with follow-ups, data tables generated and processed for statistical analysis are often of the “wide-format” type, consisting of one row per individual. However, depending on the situation and purpose of the study, they may need to be transformed into the “long-format” type, which allows for multiple rows per individual. This tutorial clarifies the typical situations wherein researchers are recommended to split follow-up times to generate long-format data tables. In such applications, the major analytical aims consist of (i) estimating the outcome incidence rates or their ratios between ≥2 groups, according to specific follow-up time periods; (ii) examining the interaction between the exposure status and follow-up time to assess the proportional hazards assumption in Cox models; (iii) dealing with time-varying exposures for descriptive or predictive purposes; (iv) estimating the causal effects of time-varying exposures while adjusting for time-varying confounders that may be affected by past exposures; and (v) comparing different time periods within the same individual in self-controlled case-series analyses. This tutorial also discusses how to split follow-up times according to their purposes in practical settings, providing example codes in Stata, R, and SAS.

Background: Although both a lower and a higher body mass index (BMI) are reportedly associated with head and neck cancer (HNC), reports from Asia are scarce. Moreover, evidence regarding the association between height and HNC is limited.

Methods: We investigated associations between BMI, height, and the incidence of HNC among 102,668 participants (49,029 men and 53,639 women) aged 40–69 years in the Japan Public Health Center-based Prospective Study. We followed participants from 1990 to 2013. We conducted a Cox proportional hazards regression analysis, which included adjustment for potential confounders, such as smoking status. Baseline weight and height information were self-reported.

Results: Over an average follow-up of 18.7 years, 311 HNC cases were newly diagnosed. Lower BMI was significantly associated with HNC, with hazard ratios (HR) of 2.75 (95% confidence interval [CI], 1.63–4.64) for <18.5 kg/m² and 1.63 (95% CI, 1.15–2.30) for 18.5–20.9 kg/m² compared to 23–24.9 kg/m². Increased risk was suggested for higher BMI, with an HR of 1.30 (95% CI, 0.84–2.00) for ≥27.5 kg/m². This trend was also observed in quadratic models. Results were similar among never-smokers. Meanwhile, only lower BMI showed a strong association with HNC risk among former and current smokers (HR 3.09; 95% CI, 1.54–6.20 for <18.5 kg/m² compared to 23–24.9 kg/m²). Height showed no association with HNC.

Conclusion: Lower BMI was significantly associated with HNC risk, while increased HNC risk was suggested in higher BMI among never-smokers. Among former and current smokers, only lower BMI was associated with HNC risk.

Background: Parents’ educational background is presumed to influence the incidence of vaccine-preventable diseases in children through their decisions about vaccinations and other family lifestyle choices. Regarding voluntary vaccination, a household’s economic situation may also be associated with non-vaccination. Therefore, this study investigated the association between parental education and vaccine-preventable diseases (varicella, mumps, influenza [flu], pertussis, measles, and rubella) in children, which currently remains elusive.

Methods: We used datasets from the Japan Environment and Children’s Study, which included 104,062 fetal records; our study population comprised 80,930 children up to the age of 3 years. The associations between parental educational background and children’s infectious diseases were examined using binomial logistic regression analysis. The mediating effects of household income, vaccination, and smoking were examined using a path analysis.

Results: For varicella, mumps, and influenza covered by voluntary vaccination, a higher education level of the father was associated with a lower incidence of infection. The association between mothers’ education and children’s infection was limited. There were both income-mediated and non-income-mediated pathways between parental education and voluntary vaccination. For pertussis, measles, and rubella, which are covered by routine vaccines, there was no association between parental education and the child’s infection.

Conclusion: An association between parental education and childhood infections was observed. Providing financial support for vaccination and communicating the benefits of vaccination in a way that parents at all levels of education can understand may help reduce the incidence of infectious diseases among children.

Background: Informal caregiving of older parents adversely affects the mental health of family caregivers. However, the psychological effects of caregiving cessation and the trajectories of these effects have rarely been examined in Japan. This study addresses this gap.

Methods: Based on a 17-wave nationwide population-based survey in Japan, we analyzed longitudinal data from 8,280 individuals aged 50–59 years in 2005 who started caring for their older parents in 2006 or later and ceased caregiving by 2021. We identified the timings of caregiving onset and cessation and examined the trajectory of psychological distress (PD), defined as a Kessler score ≥5 on the 6-item Kessler scale (range 0–24). Linear mixed models were used to assess the trajectory of PD that evolved after caregiving cessation over the subsequent 3 years.

Results: After adjusting for covariates, the probability of PD decreased by 5.6 percentage points (from 40.8%; 95% confidence interval [CI], 4.1–7.0%) for female caregivers and by 1.9 percentage points (from 31.7%; 95% CI, 0.3–3.5%) for male caregivers at caregiving cessation, remaining stable in subsequent years. For women, higher PD risks related to co-residence with a care recipient diminished quickly upon cessation of caregiving, while the unfavorable impacts of no social activity, extended duration of care, and long-hour daily care persisted in subsequent years. For male caregivers, the impact was generally more limited.

Conclusion: These results suggest that changes in mental health following caregiving cessation warrant serious consideration when developing support programs for former family caregivers.

Background: As the most common chronic liver disease worldwide, the natural history of metabolic dysfunction-associated steatotic liver disease (MASLD) in the general population is barely reported.

Methods: The Shanghai Suburban Adult Cohort and Biobank study recruited 36,404 adults between 2016 and 2017, and followed up 25,085 participants between 2019 and 2023 in Songjiang District. A questionnaire survey was conducted using face-to-face interview, and physical examination and laboratory tests were conducted. MASLD was diagnosed using liver ultrasound and the cardiometabolic risk factors (CMRF).

Results: A total of 36,122 and 21,831 participants met the criteria for baseline and follow-up analyses. The prevalence of MASLD at baseline was 36.8% overall, and 73.6% among those with a body mass index (BMI) over 28 kg/m². After a median follow-up time of 4.26 years, the incidence density for MASLD was 8.4, and the recovery density was 11.4 per 100 person-years overall and was 20.0 and 8.4 per 100 person-years for those with baseline BMI over 28 kg/m². Per 1 kg/m² increase in baseline BMI was associated with a 15% increase in incidence (hazard ratio [HR] 1.15; 95% confidence interval [CI], 1.14–1.17) and an 8% decrease in recovery (HR 0.92; 95% CI, 0.90–0.93). From baseline to follow-up visit, participants who remained non-obese or remained normal cardiometabolic status always showed the lowest incidence and the highest recovery rate, followed by those with improved status.

Conclusion: The prevalence and incidence of MASLD were high among Shanghai residents, and active recovery was also observed. Obesity was the most important risk factor, and weight loss and lipid level reduction were beneficial for preventing or reversing MASLD.

Background: This study investigated fundamental demographic variables within the Taiwan Biobank (TWBB) and compared them with national demographic statistics. Additionally, a matched cohort analysis compared TWBB participants with nonparticipants to uncover disparities in sociodemographic and clinical characteristics.

Methods: A total of 128,663 individuals aged 30 to 70 years without cancer were recruited within the TWBB, and 514,652 nonparticipants matched by age and sex were randomly selected from the National Health Insurance claims database. Sociodemographic variables, healthcare utilization metrics, underlying medical conditions, and subsequent mortality and cancer risk were analyzed.

Results: TWBB participants were more likely to be female, older, married, higher educated, with higher incomes, and urban residency. Healthcare utilization metrics showed minimal differences. Pre-cohort entry, TWBB participants had a higher prevalence of certain medical conditions, such as peptic ulcer disease, osteoarthritis, osteoporosis, and uterine leiomyoma in females. During follow-up periods, elevated mortality rates were observed among TWBB participants but decreased cancer risk.

Conclusion: The TWBB cohort exhibits disparities in sociodemographic and health-related attributes compared to the general population, comprising participants who were older, female, married, higher educated, higher income, and predominantly resided in urban areas. While mortality rates are slightly elevated within the TWBB cohort, cancer incidence rates are lower. Despite limitations in representativeness, the TWBB’s size and exposure measures offer valuable insights into associations between exposures and health conditions.