Statistical analysis
Answers were classified into two groups; participants who have no
symptom and those who have any ongoing symptoms that lasted longer than
four weeks at the time of the survey. We compared visual analogue scale
(VAS) and HRQoL values estimated by the EQ-5D-3L
questionnaire16 by Japanese value
set17 between two groups using Mann-Whitney U test,
after adjusting basic characteristics of the participants by one-to-one
propensity score matching (nearest neighbour pair matching, caliper =
0.2) calculated by multivariate logistic regression model predicting the
likelihood of having ongoing symptoms.18,19 We
included age, sex, BMI, smoking, drinking, hypertension, diabetes,
chronic obstructive lung diseases, malignancy, use of antivirals, use of
systemic steroids, and severe COVID-19 disease during admission (use of
mechanical ventilation or extracorporeal membrane oxygenation during
admission, according to the definition by a report of national registry
data in Japan20). The standardized mean difference was
used to measure covariate balance, and an absolute standardized
difference above 20% was interpreted as a meaningful imbalance.
Two-sided p values of <0.05 were considered to show
statistical significance. All analyses were conducted by R, version
4.0.5.21