Social distancing—or lack thereof—can have a huge impact on the rate of contact, or how many other people an infected person interacts with in a given span of time. Environmental factors, such as climate, population density, and landscape, also play a role in the likelihood of transmission.
The rate of transmission per contact is another variable, and can be affected by how long the virus can survive on any given surface that an infected person comes in contact with, and how far the virus travels in the air. Additionally, how long an individual is considered contagious is unknown and may vary by individual case.

The ratio of people who are infected and show symptoms versus those who do not show symptoms is largely guesswork at this point. People who are symptomatic are much more likely to seek testing and treatment, or to simply self-isolate, than people who are not. However, the unknown quantity of people who are infected but asymptomatic are still potentially transmitting COVID-19 to others.

The uncertainties detailed in the other factors play a huge role in the accuracy of reported cases and by extension, fatalities.
It’s difficult to determine fatality rate by dividing the number of people who have died by the number of people who have been infected when there isn’t an accurate count of infected individuals or individual fatalities.
Additionally, pre-existing conditions need to be taken into consideration, as rates of infection and death are going to differ in areas where chronic health problems are more prevalent. Hospital capacity also has an impact on fatality rates, as the ability to prevent death from COVID-19 or other illness depends on it.