Table 2.

Methodological limitations of published studies into post-COVID-19 syndrome.

- Diverging, non-standardised definitions
- Heterogeneous inclusion criteria
* Persistence of a single symptom vs clusters of symptoms
* Presence of organ damage vs subjective symptoms
* Non-systematic evaluation of neurological and cognitive symptoms
- Differences in the timing of assessment and in follow-up times
- Differences in the type of assessment
* Telephone interview vs physical examination
* Subjective data from digital apps
- Heterogeneous samples in terms of clinically relevant variables
* Age
* Severity (mild or asymptomatic COVID-19 / severe COVID-19)
* Sample size
- Lack of a control group