estimating with missing observations

Hi there,
two basic questions about estimating with missing observations:
1) How do I need to declare a missing observation in the data file? Is it an empty cell or some type of a character (such as "." for example)?
2) Do I need to change anything in the estimation command to alert the program that there are missing observations?
Thanks in advance!
El Chino Milton
two basic questions about estimating with missing observations:
1) How do I need to declare a missing observation in the data file? Is it an empty cell or some type of a character (such as "." for example)?
2) Do I need to change anything in the estimation command to alert the program that there are missing observations?
Thanks in advance!
El Chino Milton