Results are summarized as means ± SD for continuous variables and as percentages for categorical variables. A 2-sided probability value of <0.05 was considered to indicate statistical significance. The FMD value in subjects over 60 years old was determined to be 2.7 ± 2.5% in a previous study (29 (link)). The number of subjects needed to detect a difference of 1.0% FMD and a standard deviation (SD) of 2.5% between two groups with a probability of 0.05 and a power of 0.80 was 100 per group. Continuous variables were compared by using ANOVA. Categorical variables were compared by using chi-square test. Relationships between variables were determined using Spearman’s correlation coefficients. To create a matched cohort of control subjects and atomic bomb survivors, a propensity score was calculated using logistic regression analysis of the probability of baseline clinical variables in two models: model 1 including age and sex and model 2 including age, sex, body mass index, heart rate, hypertension, dyslipidemia, diabetes mellitus, and current smokers. To create matched pairs to investigate the associations of exposure to radiation with vascular function and vascular structure, matched pairs were using one-to-one propensity-score matching analyses. The caliper size of propensity scores was used a quarter of a standard deviation of the sample estimated propensity scores for comparison of vascular function. The data were processed using JMP pro version 15 (SAS Institute, Cary, NC, USA).
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