*3.4. Statistical Analysis*

For the purpose of statistical analysis, the study participants were divided into two groups: Group 1—professionally active participants (younger participants) and Group 2—octogenarians (participants aged ≥80 years). Descriptive statistics were based on the mean and standard deviation (SD). Student's *t*-test was used to determine significant differences between the pre-Covid-19 and Covid-19 dataset. *p* < 0.05 were considered statistically significant. Statistical analysis was performed using the Statistica 13 program.

#### *3.5. Definitions*

Throughout the text, the authors use the following terms: self-isolation and shelterin-place to denote the period of the official policy of hard national lockdown, which was introduced in Poland on 10th March 2020, due to the Covid-19 pandemic and meant a total ban on leaving home, except for the necessity to make necessary purchases, going to work, church, with a dog or taking out the rubbish. The complete lockdown policy expired after the restrictions were relaxed on 30 April 2020. All study participants were self-isolated at home during the follow-up period. All working participants (three subjects) worked remotely from home.
