Hello, consider the following paper  doi: 10.1136/thx.2006.066837
Considering the problem of external validity of RCT and inclusion and exclusion criteria, answer the following questions:
1. What do you think about the results?
2. What do you about the authors' conclusions?
3. Do you think that this situation may be similar in other clinical problems or patient populations? 
4. Can you give an example?