Statistical analysis
All statistical analyses were performed using IBM SPSS Statistics 25.0
(IBM Corp., NY, USA). Continuous data were expressed as means with
standard deviations or medians with interquartile ranges (depending on
data distribution). The Mann-Whitney U test was used to compare
continuous variables and a post-hoc analysis with the Dunn-test
and the chi-square test were used to compare categorical variables.
After adjustment for gender and
body mass index (BMI), correlations between lipid level and the SCORAD
score were evaluated by partial correlation analysis. Generalized linear
models with the logit function or gamma function (depending on data
distribution) were used to determine the odds ratios or beta values for
the relationship between lipid parameters and atopic dermatitis or
SCORAD score.
Propensity scores were used to mitigate biases arising from nonrandom
treatment assignment. Thus, for each pairwise comparison, matched
cohorts were constructed using 1:4 propensity score matching with a
caliper of 0.25 on the logit scale.23,24 A Cox
proportional hazard model was then fit to the matched cohorts using the
Cohort Method R package (https://github.com/OHDSI/CohortMethod), and the
hazard ratio (HR) and 95% confidence interval (CI) was calculated for
each outcome of interest, a procedure that reduces residual bias and
variance.25