they often ignore the person who's always grumpy.
Deciding that, that person is not going to be happy anyway,
we might as well get with the rest of us like and left them be grumpy.
This also raises the issue of manipulability.
Whether people honestly disclose their preferences or whether they instead
say something to try to get the effect that they want rather than be honest.
How does that work with the system like MusicFX?
>> Yeah, actually that came out very clearly as one of their first results.
They had this system as I mentioned where if something is hated wouldn't be used.
Sort of related to the misery approach you just mentioned.
Now, what they found would be the people would explicitly choose that hate rating
simply if they didn't especially like something.
Not if they thought it would be some better station then they said they hated
the current one, whether they hated it or not.
And consequently this system soon became unuseful.
You would soon get to a situation where no music at all could be played because
someone would have said they hated it even if no-one really hated it.
So that was a clear example of manipulation,
in fact they changed that algorithm very quickly to avoid that problem.
>> Yes I remember Joe McCarthy the person who led the effort of MusicFx telling
the story about, the people in the gym who would exercise their power
by rating something hated when it was playing so they could change the music.
And watching when they've changed the system so
that people who went to do that and tried it discovered it didn't work anymore.
Which apparently led to some people being quite disappointed that
their power had been diminished.
We should point out that that kind of manipulation occurs even in
a system like Doodle.
We probably all know people who are very accommodating and
scheduling a meeting and they will check.
I could be available all of these different times.
There are other people who say I really want to meet Wednesday
between two and four.
So those are the only times I'm going to check on the meeting form.
And it requires a social process to
figure out whether you respect those people's constraints.
Whether you cut them out of meetings if they start being too difficult to
schedule, or whether somebody has to apply social pressure to say, you know what?
You need to provide more times, you're not playing as part of the team.
So this whole problem of manipulation is a real one.
I should- >> Yeah.
>> Go ahead.
>> Sorry, and you just give it a good characterization of what a mess it can be
if people start manipulating, and even if people are aware of the problem and try to
solve it by applying social pressure in the right, it's still quite difficult.
You can't really force people to be honest, but the interesting thing is there
are some aggregation algorithms which to force people to be honest.
For example is median one has the advantage,
that no matter how evil minded you are.
You have nothing whatsoever to gain by specifying anything other than your true
preference.
Not to leave that mathematics as an exercise for
your students but if you just look through the various different cases.
You can see that you will never have anything to gain by specifying anything
other than what you really believe.
And that's the best thing because, and
you don't have to worry about all those processing that you just mentioned.
Of course it also implies that you have to convince people that it's true that they
have nothing to gain by manipulating.
The nice thing about the media, this is so
simple people may actually pretty well see what is the case.
>> So, while we talk primarily about the algorithms here,
maniputability, calculation.
We should point out that this is in a larger context that
involves specifying preferences, decision making at the end.
All of those aspects to come up with a reasonable use of a group recommendation.
And some of these will come up later in the class when we're talking with pro
approve from EPFL, whose done a lot of work in the listening preferences.
But I know that you have some thoughts particularly about interfaces and
ways of thinking more creatively about how people might express preferences.
When we're dealing with groups of people,
particularly groups of people who may already know one another.
