I need to work on a regression model to estimate the volume of individual trees of a particular species. The independent variables are the tree’s height and its diameter at breast height (DBH). How do I determine the sample size or how do I know when my sample size is sufficient for my model to accurately predict the volume of trees in my country, when the total size of the population (total number of trees in my country) is unknown. I’ve been there is a way to test my sample to know when it is big enough for the model to make accurate predictions.
My knowledge and understanding of statistics is pretty limited and I’m having a bit of a hard time understanding some material I find on the internet, so please excuse me if the question is too basic.