I have a quick question...I have a problem where I need to forecast into the future (let's say I'm forecasting population trends). So I have an equation that would use last year's population to get this year's population. I can then get next years, the year after,... However, the forecast has an error associated with it. How can I incorporate this error into my forecasting or at the very least keep track of the error (since it will compound for each successive year) so I have an estimate term and variance term in future years.