I have time-series data. It includes a number of patients with series conditions due to car crashes. After I remove the trend, I found that some number of patients becomes negatives which is impossible. What is the problem? What is my mistake? I remove the trend because I do not want to model it as a covariate. Why? because, I read that if I do not want to model the trend as a covariate, then I can remove it. What I should do to remove the negative values?
Should I remove the trend of this data? If so, how can I avoid negative values when removing the trend?