The American journal of medicine
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Review Comparative Study
Comparability of control and comparison groups in studies assessing long COVID.
Awareness of long coronavirus disease (COVID) began primarily through media and social media sources, which eventually led to the development of various definitions based on methodologies of varying quality. We sought to characterize comparison groups in long COVID studies and evaluate comparability of the different groups. ⋯ Long COVID studies in high-impact journals primarily examine symptoms and risk factors of long COVID; often lack an adequate comparison group and often do not control for potential confounders. Our results suggest that standardized definitions for long COVID, which are often based on data from uncontrolled and potentially biased studies, should be reviewed to ensure that they are based on objective data.