I have a set of CMR data and I am using the RD with Huggin's p and c with Random Effects. That model provides estimates of phi (with temporary immigration) and N is a derived parameter. I can of course estimate lambda from the N's and calculate the SEs with the delta method. My question is whether lambda and phi can then be used to calculate f (lambda-phi=f)? The problem comes with estimating the variance. I assume it is not as easy as just adding the variances because lambda and phi are clearly not independent for a given year. Is there a solution to this? Thanks!
Joe