How many times on average do people wake up per night? It would be best if the answer could be broken down by age and sex, and even by other variables (alcohol-drinker vs teetotaller, etc).

If there's a difference between self-report data and data from studies that observe people sleeping, I'm interested in that too.

This image, 



which I took from here, implies that waking up several times is normal, but the article doesn't provide any information on averages.

It may be that the median is more useful than the mean in this context.
Based on this paragraph from the Wikipedia article on hypnograms

On a hypnogram, a sleep cycle is usually around 90 minutes and there are four to six cycles of REM/NREM stages that occur during a major period of sleep.
Most SWS occurs in the first one or two cycles; this is the deepest period of sleep. The second half of the sleeping period contains most REM sleep and little or no SWS and may contain brief periods of wakefulness which can be recorded but are not usually perceived.
The stage that occurs before waking is normally REM sleep.

And this image (also from wiki):
Sample hypnogram showing one sleep cycle (the first of the night) from NREM through REM
A normal and healthy person usually wakes for a brief time after his/her REM stage was finished in each sleep cycle. So, if we consider A 7–8-hour sleep probably includes four cycles, and each cycle include at least one REM, then each person at least wake four times.