To answer your question, we are assigning each person a test version, and then tracking how they do. This is the API you call to find out what version of the page this user gets. If the user has never been assigned a test version, then they will be assigned one. The calling code does not care whether the version was newly created. But you definitely need the person in there because the test assignment is tied to the person.

About the order I gave the explanation in, I've tried explaining it both ways and had people draw blanks. Conversely I've had people find it too obvious to talk about either way.

Still I'll go through and review that section with an eye to making it clearer.

Ah, much clearer now. My problem here was that you didn't say that you were only showing the API for a central but incomplete part of the A/B-test framework, one could say the controller interface of the MVC model. The management of tests and versions, their mapping from name to webpage, the logging (for example log_test_activity()), and all the statistical analysis is (in a strict view) part of the API too.

Just mentioning in that slide that "that is the function that selects which version of a test to show a person on the website" would provide context and make this slide so much easier to understand. That sentence may be obvious to a smal l or large part of your audience but would have helped the others to keep up (at least it would have helped me, 100% of this test group ;-). It is also not the whole truth about the routine, but its possible use in the statistics phase to map users to versions can be explained later

"don't have time to do real exercises": Do you mean test presentations or Moritz suggestion to provide examples? If the latter, you don't need *real* exercises/examples. A hypothetical example can be trivial and senseless, it is a way to ground the theory in the practical.

Look at the slide "Behind the scenes". Apart from the first sentence "This does what it says" (which has absolutely no information value at all) this slide could have been replaced with an example where you provide the same information in the context of your example.

Let's say you have (on a previous slide) given the example of a english to suaheli translation page and you want to test it with versions with green and blue background color.

----------------------------------
Peters first visit
------------------
Peter visits a page -> web server calls get_or_create_test_version(<pa
+ulsid>,'EtoS',['green','blue']);<p>

New User? [small picture of file cabinet with a arrow pointing to a '?
+'] YES.
[small picture of a dice or coin toss] -> random choice of 'green' or 
+'blue'. Let's say 'green'. ->
[picture of string 'peter has green' with arrow to file cabinet ]. 

$version='green'

[ small picture of a green cube which looks like a webpage ]

----------------------------
Peters next visits
----------------
Peter visits a page --> web server calls get_or_create_test_version(<p
+aulsid>,'EtoS',['green','blue']);

New User? [picture of file cabinet with an arrow to string "peter has 
+green"] NO.

$version = 'green'

[ small picture of a green cube which looks like a webpage ]
------------------------
[download]

Yes, this is trivial (and could be improved a lot). But this gives the same information as the replaced slide and because of the pictures and the concreteness is faster and easier to understand and remember.

I don't think that a picture on every slide is beneficial. This will distract many with questions like 'What has that picture to do with the message of this slide?', especially with long presentations. I would put pictures into introducory, title/heading/opening/closing slides (slides 0 and 47 for example) and easy/low complexity slides (slide 4). On all other slides there should be a picture only if it either:
1) contributes to the information on the page (slide 5 is a positive example), or
2) loosens up the presentation by showing a cartoon, a famous saying or a funny picture that has some relevance to this slide. This cartoon or picture must be the first thing on the slide (because it is eye-catching, everyone will read or look at it first) and you have to give the listeners time to view and possibly laugh about this picture.

Disclaimer ;-): All of this IMHO. And apart from the above I like your presentation and find it interesting, but you wanted to know about the bad not the good parts.

I was up until 2:30 this morning putting pictures in slides, I'm not taking them out without good reason. Perhaps once I have more sleep I'll reconsider and change my mind, but at the moment they seem to have a purpose to me, if only to convey a particular emotion or remind people of the earlier slides which connect to the current ones.

I'll definitely rework the behind the scenes slide. I don't think that I'll quite go with your idea, if only because I don't have a store of clip art I could use to draw that picture. But I will try to find a way to make that slide do more to justify its existence.