One measure of anxiety is how often a person blinks. Men tend to blink a bit less often than women. When the heath of the eyes are good and the air is adequately humidified, men on average blink once every 7 - 8 seconds whereas women on average blink every 5 - 6 seconds. There is a fair amount of variability between one person and another though. But if the rate of blinking increases - or if in an absolute sense, the blinking frequency is high, this is a very reliable body language signal of nervousness.
In this video segment in the Republican Presidential Debate last night, the four remaining candidates can be seen introducing themselves. Ron Paul first, followed by Rick Santorum, then Mitt Romney and finishing with Newt Gingrich. Paul's and Gingrich's blink rate were not increased over baseline normal. However Santorum's and Romney's blink rate are dramatically increased. All four candidates have considerable debate experience as well as national television exposure .... so why are two of them nervous? Since Romney and Santorum are the front-runners and most pundits feel that one of these two will most likely be the Republican Presidential candidate - one conclusion that we can draw, is that Mitt and Rick have the most to lose by a poor performance. After all, Super Tuesday awaits.
Blink rate can be used to assess nervousness in other contexts. When a person tells a lie, especially if the ramifications of being caught in the lie are more extreme, an increase blink rate is a very reliable indicator of their level of anxiety.