I agree! how ever any specific reason behind selecting the group having lowest odds as reference? Even if a statistical software can help in getting the results, but it would be great to hear from you if there is any concept behind.Please do reply.
The reason typically is that most people have difficulty interpreting protective ORs, those under a value of '1'. Also, if your scenario above is what you plan to do, you may have some type of immortality bias or survival bias. The rate of smoking in older persons may be higher, but the smoking based sequelae may have manifested itself and they die (lost to follow-up) or are less likely to provide info since they are institutionalized. There are impacts from smoking.