Authorship should be limited to those who have made a significant contribution to the concept, design, execution or interpretation of the research study. All those who have made significant contributions should be offered the opportunity to be listed as authors. Other individuals who have contributed to the study should be acknowledged, but not identified as authors.Some reasons why someone should not be a co-author:
- All they did was obtain the funding for the project.
- Their only contribution is that they are the official supervisor of a student who is a co-author.
- They have not read the paper!
- Their only contribution is that their status in the field may help get the paper published.
- They are not confident the results are valid. In particular, they cannot claim the future option of saying, "Well I didn't work on that part. I always had my doubts about that part..."
This article on physics postdocs perceptions of the issue is worth reading.
When in doubt ask your supervisor to discuss these issues.