Every time I think I know what's going on, suddenly there's another layer of complications.
https://rpubs.com/enwuliu/1264909
https://enwuliu.shinyapps.io/detectOR/
https://rpubs.com/enwuliu/1209721
https://rpubs.com/enwuliu/1204019
https://rpubs.com/enwuliu/1198953
RPubs - Notes for selection model and mixture pattern model
https://rpubs.com/enwuliu/1183239