Yet More Deceptive Graphs
As you've probably heard, there was a horrible incident in Pittsburgh this weekend, in
which a crazed white supremacist who believed that Obama was coming to take his guns shot and
killed three policemen. Markos Moulitsas, of Daily Kos, pointed out lunatics like this shooter
are acting on conspiracy theories that are being relentlessly promoted by the likes of Glen
Beck and Michelle Bachman. It's not an unreasonable thing to point out, given the amount of
time that Beck and Bachman have spent lately talking about the impending socialist/fascist
crackdowns that will require a revolutionary response from all right-thinking patriotic
Now, you may think that Kos is an idiot. In fact, even though we agree on many
political issues, I think that Kos is an idiot. I (obviously from what
I wrote above) happen to agree with the basic hypothesis that if you tell
people that the government is going to come and get that and that they need to
defend themselves, that some people are going to believe that the government is
coming to get them and that they need to defend themselves. But the way
that Kos responded was disgusting; it was latching on to a tragic event in
a shallow, snide, heartless way.
But whether you think Kos is an ass ore not isn't the point. Regardless of your opinion of
the man, there's no arguing the fact that he's created a website that draws a really
astonishing amount of traffic, and has become a nexus for many activists on the political
And that, in turn, naturally draws hatred and mockery from the political right. Because,
you see, no one who disagrees with those fine patriotic folks could possibly be an
honest, serious person. They must be a bunch of scheming bastards, obviously.
So, when Kos came out bitching about how the rantings of various crazies really do
have a connection to the actions of people like the Pittsburgh killer, naturally it couldn't be that he actually believed that people ranting about how the President is
creating a fascistic tyranny that's going to come take all of your guns could actually
inspire a crazy person to believe that the President creating a fascistic tyranny that was going to come and take away his guns. No, that couldn't be. He must be up to something - like trawling for hits!
Which, finally, brings us to our topic.
A conservative blogger named Moe Lane posted his theory about why Kos spoke out about the Pittsburgh shooter. It's because his pageviews have declined so much. But, of course, it wouldn't be good enough to just say that DKos pageviews are down - he's got to show that it's specific to those dirty liberals. So he produces two graphs - one for DKos, and one for RedState, a major conservative site. Here are his graphs; DKos first, Redstate second:
A quick glance shows that both had a huge spike right around the elections, and then they
dropped off pretty dramatically. Then both had a slow upward trend. But the RedState trend
looks a lot steeper.
What you won't notice in a quick glance is that the scales are totally different. The DKos scale runs to 80 million hits in October '08; the RedState scale runs to 3 million hits. The absolute increase in hits per month since the election is
actually larger at DKos than at RedState. The DKos increase per month since December is over a million pageviews; the total increase in pageviews at RedState over
those four months is around 1/2 a million.
This is a very common problem in published graphs. It's often done by mistake: if you use
a tool like Excel, and tell it to plot data, it will automatically select scales based on the data. If you're clueless, and you do things the most naive way, you'll wind up
with two graphs that are, individually, perfectly accurate; but taken together, are
On the other hand, it's also a common misleading tactic. People mess with scales
to produce very misleading results all the time. For two graphs to be meaningfully comparable, they need to have the same zero point, and the same scale. So if you're going to use graphs for comparison of two sets of data, at a minimum, you need to make sure that you match the axes - both the zero points and the scales. Better, if comparison is the goal, then
you should plot both sets of data on the same graph.
To give you a sense of how the data actually compares, I took the two charts posted
by Moe Lane, and eyeballed them to try to get numbers, and using Google Docs, I combined those numbers into one graph. Here's the result.
There are two interesting things about that graph. One is just how badly DKos traffic dwarfs RedState. The two really aren't comparable. When you look at website traffic on
community-oriented sites like DKos and RedState, you get vastly different behaviors
at different scale. It's not fair to RedState to compare it to DKos - in community oriented sites, size begets size, and RedState simply isn't close enough to DKos to be able to
sustain the comparison. But if you insist on making it, the one relevant comparison would be
the slopes of the increase lines from December to now. I don't know how to superimpose it
on the graph (I'm not a GDocs wizard), computing a best-fit line to the four
points does produce a slightly steeper slope for Redstate - about 1.11 to 1.07. (And that's
being a bit generous in the computation; I can't really claim to have more than
two significant figures in my measurements; but those slopes are 3 sigfigs each.) In other
words, the growth rates are, pretty much, equivalent. In fact, overall, they track each other extremely well - each bump, each dip, appears in both graphs. The exact month-to-month pageview ratios vary somewhat, but overall they're pretty similar.
Which isn't exactly what Mr. Lane tried to suggest.
I actually think that in this case, he's just clueless. Those graphs look almost exactly like the graphs produced by sitemeter, a common web-service that monitors pageviews
on a website. I think that he just looked at the pageview graphs for the two sites, and
really genuinely thought that they were comparable.