Can we do tsappend with some formula. Suppose we have yearly time series up to 2019. I extend 4 observations. So 4 missing values generated. Now I want to fill it considering moving average of last 3 years. So if the variable is growth, then 2020 growth will be average growth of 2017, 2018, 2019./ 2021 growth will be average growth of 2018, 2019 and 2020. How to write the command without typing in data editor of STATA.