MATT CUTTS: OK.
Today's question comes from Vancouver.
Jzbecker wants to ask, under which circumstances will
Google decide to display multiple results
from the same website?
It's a really fun question, because the answer has changed
over the years.
But the high level answer is, when we think it's useful and
it doesn't hurt diversity too much.
So let's look at the interplay between those two factors.
Let me talk about a system that we used for years and
years and years, like since I joined Google, this long.
There was something called host crowding.
And what host crowding did is, suppose you had one result
that showed up from example.com
in the search results--
these are search results--
and another example that also showed up from example.com.
So what host crowding basically said is, OK, to make
things a little bit more easy for the user to parse and read
through, let's take anything that's on that first page, and
we will indent it under.
So you'd have two results from example.com, and the second
one would just be indented a little bit
underneath the first one.
That makes it easier for the user to visually group those
results and know, oh, these are both from example.com.
It's safe to say that we've done a bunch of different
experiments.
Host crowding lasted for a long, long time.
And it was really, really nice because you'd often have a see
more results from example.com.
So you could click that, and you can do
an even deeper dive.
But it was also very nice because it ensured diversity.
That is, if you had seven or eight results from GeoCities,
sometimes that can crowd out other good results.
And so you could see a couple of the best ones from
GeoCities, but then you'd also get diversity.
You'd get the rest of the results showing all sorts of
nice things along those lines.
Now what's the limitation of that?
Well, host crowding, if you only allow two results, that's
kind of a hard limit.
Sometimes it might be more appropriate
to show more results.
Sometimes it might be appropriate to
only show one result.
And host crowding was a little bit limited in that respect.
So that was one thing to consider.
The other thing is it also messes with the UI just a
little bit.
Because once you get used to the indentation, it's really
nice, but it limits your ability to do
other sorts of things.
It limits your flexibility a little bit.
So it was very nice for the time.
It was a radical improvement over many search engines that
might return 60 results from one site by
grouping them all together.
But we've sort of evolved in our thinking over time.
So the sorts of things that we have done after host crowding
include deciding to show multiple results.
So maybe you're willing to show a few or
even several results.
But then over time, it gets harder and harder to see
results from that particular host name.
And that can be kind of useful, because if you search
for antique green glass, you might get eight
results from one site.
And if that's the best site in the world to get results from,
then that's fine.
You might want to see that.
But if it's not really a great site, as far as you don't want
eight out of the top 10 to belong to that site, then if
it gets a little bit harder for each subsequent result to
show up, then you'll get you tune it, so that you get as
many as you think is useful.
And then you start to get diversity after that.
And you start to get good stuff.
Just to jump back to host crowding just for a second.
There was also the fact that host crowding, by definition,
is on hosts.
And so at least for a while, if you had a different
subdomain, then you had a different host name.
And so a few people would try to make multiple subdomains on
the same domain to try to get around host crowding and try
to get as many results as they could.
So for a while, people used to think, oh, I'll just make a
whole bunch of subdomains, and I'll get around host crowding.
And that's the sort of thing that is still not a good user
experience, because it hurts the diversity for users.
So let me talk a little bit about the way that we think
about diversity and the number of results you can see from
one website right now.
You want to show as many results as
you think is useful.
And that's the tricky bit.
What the user is looking for can vary depending on what
they're searching for.
For example, if they type in something like HP or IBM,
probably a lot of pages or a lot of results from HP is a
good answer.
So several people have noted that it's possible to get more
than two, more than four, lots of results from Hewlett
Packard if you search for HP.
But that's OK.
The user has indicated that's their interest
by doing that query.
But in general, what we try to balance is this trade-off
between a good diversity of results, because you don't
know exactly what the user was looking for.
So you want to give them a little bit of a sampling to
say, OK, here's a bunch of different possible
interpretations.
Here's what you might be looking for.
And then we also want to absolutely give the results
that we think match the query well.
And sometimes that can be from multiple pages
within the same site.
So there's always a tension.
There's always a trade-off in trying to figure out what is
the best set of search results to return.
There's no objectively true or perfect way to do it.
We've varied our scoring.
We've varied our user interfaces.
And if there's one thing you can count on, it will be that
Google will continue to test out ideas.
Google will continue to evolve how often we think it's
appropriate to show how many results from how many sites in
the search results.
But that gives you a little bit of the insight about what
we're thinking about, why it's sometimes a good experience,
and why sometimes it's not as helpful for users to see a lot
of results from the same site.
Thanks very much.