Sleep quality (PSQI), severity of insomnia symptoms (ISI), and inclination to Morningness–Eveningness (MEQr) for elderly and young respondents during the COVID-19 lockdown. Center lines show the medians; box limits indicate the 25th and 75th percentiles; whiskers extend to 5th and 95th percentiles, dots represent outliers; crosses represent sample means. Significant differences of Kruskal–Wallis test between elderly (violet) and young (yellow) participants are indicated with asterisks (*** p < 0.001). Abbreviations: PSQI, Pittsburgh Sleep Quality Index; ISI, Insomnia Severity Index; MEQr, Morningness–Eveningness Questionnaire-reduced version; N.S., not significant.