I am having difficulty understanding random stratified sampling when there are nested categories within them. Take for instance a size of 1000, and you are interested in sampling gender and smoking. Lets assum there are 500 females, so does that mean you create a first gender stratum with 500 females and 500 males. Subseqeuntly you randomly select participants from each gender category, and then create a second strata within each gender categories for smoker vs. and non-smoker. Then you select a random sample from each of these cateogory. Is that how stratified random sampling works? Because that sounds like multi-stage sampling to me? Please help I'm trying to visualise how it all works.