Hi!

in short:
- What is the best way to look at prevalence in a dataset utilizing a questionaire and diagnostic criteria?
- How can I convert "missing values" to zeroes in a variable that I created?

I am doing a epidemiologic study looking at the prevalence of a disease. The participants have filled out a questionaire that utilzes a set of criteriae, that can be used as positive diagnostic criteria for this disease. My thought is that I should create a new variable that is =1 when the criteria is meet, and then look at the prevalence in the different age-groups. Is this a good way to go? I managed to make this variable. So now every participant has either a 1 or a "missing value", and I am not getting the calculations to work properly with this value. How can I exchange the missing values for 0?

Thank you in advance