I am studying the hospital visitation from 2019 - 2021, and found that the total visits counts in 2021 Month Patterns drop a lot. For example, the visitation in January in these three years decrease about 30%. Is it there a change in sampling rate in 2021? If so, how to make the annual data comparable?
These drops in traffic could be related to the COVID-19 pandemic. Even though hospitals may have seen an increase in patients they were restricting visitors, which may explain the decrease in visits. I also recommend reading through this post for another explanation.