When thinking about potential topics for your dissertation there are two sources for ideas: experience and previous research.
What you have experienced in your professional career can be a good source of ideas. As an example, let's say that you are aware of a particular sub-group within your student population that has dropped out at a higher than average rate. This might lead to a topic on student retention for people in that sub-group.
Another great source of ideas is previous research. All the articles, books, theses, and dissertations you have been reading can suggest topics that you might want to learn more about. Perhaps you read a study on student persistence conducted at a East-Coast school and you wonder if the same results would hold true for students in South Dakota.
How can you choose a good topic. Here are some things to consider when choosing a topic.
10. A topic that will change the world.
9. A topic no-one has ever researched.
8. A topic that will help solve a problem in your current school.
7. A topic that your advisor is interested in.
6. A topic that relates to your current job.
5. A topic that will relate to a job you would like to have.
4. A topic that you are interested in.
3. A topic that you will still be interested in after working with it over an extended period of time.
2. A topic that others have already written about.
1. A topic that is completable, and completable within the time frame for when you plan to graduate.