How to answer questions in a conference talk that I should know the answer to, but don't? In a few days, I will be giving my first conference talk. I have only spent less than a year in the field, and the talk will be attended by several well-known researches, who are familiar with all of my advisor's work and all of the other literature in the area as well. Of the people in the room, it is probably them who will be listening most intently -- but it is also them who I feel the least well-equipped to answer questions from.

The questions I am most worried about will be about related work. Take it as a given that:


I clearly should know the answer to the question, because the related work is very relevant at a surface-level. Indeed, my advisor is familiar with the work and has told me to try to be prepared for any questions about it.
But I don't know the answer, because I failed to sufficiently prepare. Or, to make some excuses, maybe I am relatively new to the field and have not had a chance to read every paper in full detail. Of course I have tried some to read through this work, and I have gotten from my advisor some idea of how it compares, but I am not nearly so familiar as I should be.


It seems likely that a poor response to such a question will make me come across as incompetent, unfamiliar with related work in the field, and even unfamiliar with the context of our own work. Similarly, this may damage the reputation of our research itself. How can I best respond to such a question, so as to minimize the damage?
It will depend on the research field but there are ways to get out these situations quite well, in most cases. I also don't see any problems in admitting you don't know the answer.

Usually you won't get questions exam like style. No one will ask you:


  What's the formula for calculating XY?


Here some types of questions I've heard a lot before and some simple answers you can give without talking about the subject:


  Have you tried to use this approach? 


In that case you can answer with


  No we have not but thank you for your input, we will look into this!


If the question is:


  [Name] has used this approach, how does it differ from yours?


You can, again, simply answer with


  I am not familiar with this work but I will look into that.


The following question is tricky:


  I think there might be a problem with this part of your work, can you comment on this?


Here of course you somehow have to defend your own work and this is the part you should know. What I would do is ask the person who asked the question if I understood it right (a lot of the time that's a problem) and then if you still don't know the answer you can eitehr go with something like before


  We haven't investigated this yet, we will have to look into this in detail, thank you for your comment.


or you shift the whole discussion to a more "private" setting:


  This is an intersting point, maybe we could discuss this after this session? (in view of the time)


This is quite common to do and usually there's only time for a few short questions.

The same is true for a question like:


  Why did you use this method?


where it's easy to shift the discussion to after the session.

Whatever you do, don't try to hide the fact that you don't know the answer with strange answers. At the last conference I attended a speaker answered every question with:


  This question is spot on, but the project is still ongoing and there's a patent filed and I don't know if I can reveal that right now.


Which told anyone in the audience: that guy has no clue.