Two part model question - How to combine models?

Hi,

I have a quick question. I have a response variables that is
positively skewed and contain a substantial proportion of zeroes.
Since a common method for analyzing this type of data is a two-part
model I have the analysis of three stages:
The first involved creating two sets of data from the original: one
showing whether or not the problem is present and the other indicating
the "level of the problem" when problem is present.
The second stage involved modelling occurrence of problem, using
logistic regression, and separately modeling the level data using
ordinary regression.

Finally, the third stage should be combining the two models in order
to estimate the expected "level of the problem" for a specific set of
values of possible predictors.

My question is how to do this? IS it just enough to multiple
probabilities using conditional probabilities rule?

Thanks,
Tash

.

Loading