Statistical analysis

The relationship between anthropometric characteristics and habitual alcohol use and gait parameters at a BrAC of 0.00% and 0.11% was tested by Spearman’s Rho (0.00–0.19: very weak, 0.20–0.39: weak, 0.40–0.59: moderate, 0.60–0.79: strong, 0.80–1.00: very strong correlation).

We performed a multivariate analysis (two-way MANOVA) for forward and backward gait to reveal potential factor interactions. The two independent variables (IV) were gender (male, female) and breath alcohol concentration (BrAC; 0.00%, 0.11%). We used the twelve gait parameters of forward and backward gait as dependent variables (DV). Due to the violation of assumptions, we used Pillai’s trace results for multivariate tests.

Most of the variables did not meet the assumptions of normal distribution tested by the Shapiro–Wilk test. The Mann–Whitney U test was used to compare the differences between genders when walking forward and backward during the data collections at a BrAC of 0.00% and 0.11% and to compare the characteristics of the participants. The Wilcoxon Signed Ranks test was used to compare the differences between sober (0.00% BrAC) and intoxicated (0.11% BrAC) conditions. Bonferroni correction (α_Bon = 0.0042) was applied to an overall α level of 0.05 to avoid Type I error.

To reduce the risk of the first type of error, we further calculated the effect size index r, which reflects the empirical basis of the effects of the real population^30,31. The magnitudes of the effect size index r can be interpreted as a small effect (r = 0.1), a medium effect (r = 0.3) or a large effect (r = 0.5)³⁰. SPSS Statistics (IBM Corp. Released 2021. IBM SPSS Statistics for Windows, Version 28.0. Armonk, NY: IBM Corp) was used for the statistical analysis.

The relationship between the subjective drunkenness score and differences in gait parameters recorded at a BrAC of 0.00% and a BrAC of 0.11% was tested by Spearman’s Rho.