I have downloaded an extract for these years: 2001 to 2015 - ACS. But in the place of brith ( bpl) variable there are only around 1 000 people and none from India which is the population I am trying to study. Why this is happening?
Which statistical tool are you using to analyze the data? There should be very few cases of missing BPL. Furthermore, here is a tabulation (from Stata) showing the counts (unweighted) with BPL == 521 (India):
It may be the case that your data was not fully unzipped/not fully loaded or that you have an error in your code. Try reloading your data and re-analyzing it without any prior manipulation.