Hello anyone

I am using stata for social science research.

I want to conduct survival analysis form longitudinal survey data on university students. I understand the theory of the analysis, but i am confused about an aspect of preparing the data for analysis. I have collected data about reasons for dropout in a survey, distributed to the same students two times during their study period. In this period, they either persist og drop out.

1. How do i merge the to survey datasets, telling stata that data from the second dataset is a second measurement of the same variables as the one in the first dataset, and;
2. how do i include the change in these variables, in my survival analysis?

I have not included examples, since this is merely a questions about preparing the data, and not how to conduct the analysis itself.