How long do you wait for a question to be answered?

I teach classes. I ask questions in class. I wait for answers. All faculty do this, so who cares. If you are in a class or teaching a class, how long do you wait for someone to answer your question? Well, I asked two questions of my class this week.
1. Estimate how long I wait when I ask you questions.
2. How long should you (ideally) wait in a class for someone to answer?
Here is the data I gathered: (and I will tell you how long I actually wait)

This is a class of about 30 students. Below is a histogram of how long they estimate I wait for an answer. To make things work out, I converted all of their responses to seconds:
This is an average of 74 seconds.

How long should I (or you) wait? (this is a class for students that are going to be elementary education teachers).
Here the average is 56 seconds. Notice that as a class, they think I wait longer than I should. I know what you are thinking. Alright already, how long DO you wait? Typically, I only wait 15-20 seconds for a response. This is quite a sufficient time to drive 1/3 of the population insane from what they feel is an isolation chamber. Really, you can tell that some people can't take the silence. I would wait longer, but usually someone will crack before that.

There was a study (that I can't find right now because I am trying to finish this before the hurricane) that said the average wait time in university lectures was 1.5 seconds. I looked at this when I observed other faculty. For this one guy, his wait time was under a second. It's kind of funny. When I teach, I have to make myself count to keep the silence. Often I will think of something completely different to help me wait.

Here is one more graph. What is the difference between how long students think I SHOULD wait and how long they think I do wait.
From this, it looks like there are many students that think I am waiting the correct amount of time (the difference is zero). There are a few that don't think I am waiting long enough - from the graph, this is 6/30. The average difference between how long they think I should and do wait is -20 seconds. So the average estimate is that I wait 20 seconds longer than I should.

Conclusion:
You need to give students time to think about a question. I would say at LEAST 30 seconds. Students can't handle the silence.