This is the analyses of the use of the PCFS in the field. This analyses includes a systematic review of the literature, as well as a survey amongst heavy users. The following files can be found on the PCFS page on OSF (Please note that none of these files are peer-reviewed): - [summary and lessons learned][3] which provides the main findings for future users, - [slidekit][4], which has more information and graphics, but might be difficult to understand without a full knowledge of the methods/report, - [full report][5] from the study, - [preregistered study protocol][6]. Based on our findings, we have drafted 10 lessons for future users, which are: 1. Since the PCFS is already translated to multiple languages by researchers and healthcare professionals working with COVID-19 patients around the world, please ensure that you are not wasting resources by executing an additional translation. The methodology, quality as well as validity of these translations need to be assessed on a case by case instance. 2. Remember that the PCFS should not be used as a stand-alone measurement instrument and is preferably supplemented with other patient-reported outcome measures. 3. Be careful of assessing the PCFS in patients with existing functional disabilities, prior to COVID-19 infection, in clinical settings. Consider asking for pre-covid limitations when the goal is to assess functional status progression over time. 4. Be careful not to mix different methodology for one assessment within one study. Mixing the questionnaire, flowchart and/or interview in one study will lead to varied results. The same goes for the variation in the included patients: the larger the variation in the included study population, the more difficult to interpret and extrapolate the results of your study. 5. Keep in mind that in research settings, patients who have died should also be assessed and marked as grade 5 to prevent selection bias. 6. Keep in mind that in research settings, the time window of one assessment should be as tight as possible to minimize variation. 7. If performing a regression analysis with the PCFS, which is an ordinal scale, as an outcome, an ordinal logistic regression (or a similar technique that maintains the ordinality of the outcome) is the most appropriate analysis. 8. Remember that it is crucial to report the methodology, time window and analysis of the PCFS in research settings in order to ensure transparency and reproducibility of work. 9. Remember that certain aspects of the psychometric properties of the PCFS have been assessed in some studies, some have not. The available evidence cautiously suggests that the PCFS measures the functional status of patients reliably and in a meaningful manner. 10. Keep in mind that the PCFS scale is completely free to use and is licensed under CC-BY-4.0. Always mention the PCFS resource page on OSF (https://osf.io/qgpdv/) or at the minimum refer to the original publication. [3]: https://osf.io/h5equ/files/osfstorage/63b6a9bc202f1709aba6b964 [4]: https://osf.io/h5equ/files/osfstorage/63b6a9c63312f108fa6888ed [5]: https://osf.io/h5equ/files/osfstorage/63b6a9c3202f1709a8a6b3cb [6]: https://osf.io/h5equ/files/osfstorage/621caf2e19ba8b0819e12df6