There is variation from state to state, but doctors tend to evaluate the following types of factors in determining whether or not you can make decisions for yourself:
- whether you can understand what the doctor is telling you and the consequences of any decision you make
- whether you can make a decision based on the doctor's information and
- whether you can tell your doctor what you've decided. This doesn't have to be verbal communication. Any expression of your desires will be sufficient (including a nod or other acknowledgment)
After your doctor has made this determination, most states require this decision be explained in writing before any medical treatment decision can be made.