I am new to Time Series Data and this question is confusing me, as I have received different advice and was wondering if I could request clarification.
I am attempting to test whether the creation of a particular type of school affects the number of rich or poor children in surrounding schools
I have 6 years of data on this, and I was doing a regression along the lines of the number of disadvantaged students, against if there is one of these schools nearby, with a number of other control variables.
Because it was a times series data I was recommended to use a lag of the dependent variable [L.] (since presumably the current number of students will impact next years')
But I was also told to use the D. operator in Stata, by others, to account for any changes in number of such groups between the years, & my search on the web / textbooks has not been overly helpful about which to use in this situation if any at all.