I love the discussion on the statistical power of the findings and the appropriate interpretation of those numbers. However, there is a much larger problematic aspect to this paper that is subtle but critical and is being overlooked in this discussion. Once you understand this bias you will realize that the paper's reported findings are most certainly dramatically understated.

Put simply, not every single patient in the study was appropriately tested for myocarditis and/or pericarditis. The statistics provided by this retrospective cohort study depend on the outcome of patients traversing the healthcare system of the population in question. These statistics are really telling you the outcome of multiple probabilistic events (listed below). Once you think through each of these events, it quickly becomes apparent that all of the biases lead these conditions to be dramatically undercounted.

1. Patient sought healthcare
2. Patient reported symptoms doctor could identify as potential myocarditis and or pericarditis
3. Doctor recognized symptoms
4. Doctor ordered appropriate diagnostic testing
5. Radiologist recognized the condition.

Let's look at each of these.

1. Given this was a retrospective study, we know that (1) happened 100% of the time. No problem here.

2 and 3. A patient with myocarditis may have one or more of the symptoms below. Some of these symptoms, such as swelling in the lower extremities, are likely a dead give away. However, most are extremely common in COVID.

- Signs of a viral infection, such as body aches, joint pain, fever, headaches, vomiting, diarrhea or a sore throat.
- Rapid or abnormal heart rhythms (arrhythmias).
- Chest pain.
- Shortness of breath, both at rest and during physical activity.
- Swelling of your lower extremities (legs, ankles and feet).
- Fatigue.

I would wager that most patients who demonstrated one or more of these symptoms indicative for potential myocarditis/pericarditis were not actually tested for the disease. To get tested, a patient lacking extreme myocarditis would likely have to push and push hard to get the doctor to test. This *heavily* biases the results toward under counting.

4. Diagnosing COVID-caused myocarditis and pericarditis is hard. The typical standard of care, at least in the US, is an echocardiogram. This diagnostic ultrasound can indeed pick up some forms of the disease but multiple papers have shown that COVID-caused myocarditis and pericarditis can be invisible on an echocardiogram. The definitive scan is a specialized MRI machine capable of a particular scan sequence. This machine is hard to find even in major health centers (there are three of them total in the Washington DC area). The cost of an MRI is at least an order of magnitude more than an echocardiogram. The echo takes about 15 minutes whereas the cardiac MRI is about 90 minutes. Thus, it is highly unlikely that the doctors in question ordered the appropriate test that can actually detect the disease in question. This further biases the findings in the same direction.

Finally, the study looks at patients from March 2020 and January 2021. The fact that COVID myocarditis and pericarditis can typically only be resolved on a specialized cardiac MRI was not common knowledge for most of the study period.

Thus, the conclusions from this study are DRAMATICALLY underestimated.