{"id":763,"date":"2009-04-06T13:40:03","date_gmt":"2009-04-06T13:40:03","guid":{"rendered":"http:\/\/scientopia.org\/blogs\/goodmath\/2009\/04\/06\/more-deceptive-graphs-scales-matter\/"},"modified":"2009-04-06T13:40:03","modified_gmt":"2009-04-06T13:40:03","slug":"more-deceptive-graphs-scales-matter","status":"publish","type":"post","link":"http:\/\/www.goodmath.org\/blog\/2009\/04\/06\/more-deceptive-graphs-scales-matter\/","title":{"rendered":"More Deceptive Graphs: Scales Matter"},"content":{"rendered":"

Yet More Deceptive Graphs<\/p>\n

As you’ve probably heard, there was a horrible incident in Pittsburgh this weekend, in
\nwhich a crazed white supremacist who believed that Obama was coming to take his guns shot and
\nkilled three policemen. Markos Moulitsas, of Daily Kos, pointed out lunatics like this shooter
\nare acting on conspiracy theories that are being relentlessly promoted by the likes of Glen
\nBeck and Michelle Bachman. It’s not an unreasonable thing to point out, given the amount of
\ntime that Beck and Bachman have spent lately talking about the impending socialist\/fascist
\ncrackdowns that will require a revolutionary response from all right-thinking patriotic
\ncitizens.<\/p>\n

Now, you may think that Kos is an idiot. In fact, even though we agree on many
\npolitical issues, I<\/em> think that Kos is an idiot. I (obviously from what
\nI wrote above) happen to agree with the basic hypothesis that if you tell
\npeople that the government is going to come and get that and that they need to
\ndefend themselves, that some people are going to believe that the government is
\ncoming to get them and that they need to defend themselves. But the way
\nthat Kos responded was disgusting; it was latching on to a tragic event in
\na shallow, snide, heartless way. <\/p>\n

But whether you think Kos is an ass ore not isn’t the point. Regardless of your opinion of
\nthe man, there’s no arguing the fact that he’s created a website that draws a really
\nastonishing amount of traffic, and has become a nexus for many activists on the political
\nleft.<\/p>\n

And that, in turn, naturally draws hatred and mockery from the political right. Because,
\nyou see, no one who disagrees with those fine patriotic folks could possibly<\/em> be an
\nhonest, serious person. They must<\/em> be a bunch of scheming bastards, obviously.<\/p>\n

So, when Kos came out bitching about how the rantings of various crazies really do
\nhave a connection to the actions of people like the Pittsburgh killer, naturally it couldn’t be that he actually believed<\/em> that people ranting about how the President is
\ncreating a fascistic tyranny that’s going to come take all of your guns could actually
\ninspire 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!<\/p>\n

Which, finally, brings us to our topic.<\/p>\n

A conservative blogger named Moe Lane posted his theory<\/a> 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:<\/p>\n

\"dkos-300x244.jpg\"<\/div>\n
\"rs-300x244.jpg\"<\/div>\n

A quick glance shows that both had a huge spike right around the elections, and then they
\ndropped off pretty dramatically. Then both had a slow upward trend. But the RedState trend
\nlooks a lot steeper.<\/p>\n

<\/p>\n

What you won’t notice in a quick glance is that the scales are totally<\/em> 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
\nactually larger<\/em> at DKos than at RedState. The DKos increase per month since December is over a million pageviews; the total<\/em> increase in pageviews at RedState over
\nthose four months is around 1\/2 a million.<\/p>\n

This is a very common problem in published graphs. It’s often done by mistake: if you use
\na 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
\nwith two graphs that are, individually, perfectly accurate; but taken together, are
\nvery misleading.<\/p>\n

On the other hand, it’s also a common misleading tactic. People mess with scales
\nto 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
\nyou should plot both sets of data on the same graph.<\/p>\n

To give you a sense of how the data actually compares, I took the two charts posted
\nby 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.<\/p>\n

\"dkos_vs_redstate.png\"<\/div>\n

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
\ncommunity-oriented sites like DKos and RedState, you get vastly<\/em> different behaviors
\nat 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
\nsustain the comparison. But if you insist on making it, the one relevant comparison would be
\nthe slopes of the increase lines from December to now. I don’t know how to superimpose it
\non the graph (I’m not a GDocs wizard), computing a best-fit line to the four
\npoints does produce a slightly steeper slope for Redstate – about 1.11 to 1.07. (And that’s
\nbeing a bit generous in the computation; I can’t really claim to have more than
\ntwo significant figures in my measurements; but those slopes are 3 sigfigs each.) In other
\nwords, 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.<\/p>\n

Which isn’t exactly what Mr. Lane tried to suggest.<\/p>\n

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
\non a website. I think that he just looked at the pageview graphs for the two sites, and
\nreally genuinely thought that they were comparable. <\/p>\n","protected":false},"excerpt":{"rendered":"

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 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[8],"tags":[],"class_list":["post-763","post","type-post","status-publish","format-standard","hentry","category-bad-statistics"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p4lzZS-cj","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"_links":{"self":[{"href":"http:\/\/www.goodmath.org\/blog\/wp-json\/wp\/v2\/posts\/763","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.goodmath.org\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.goodmath.org\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.goodmath.org\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.goodmath.org\/blog\/wp-json\/wp\/v2\/comments?post=763"}],"version-history":[{"count":0,"href":"http:\/\/www.goodmath.org\/blog\/wp-json\/wp\/v2\/posts\/763\/revisions"}],"wp:attachment":[{"href":"http:\/\/www.goodmath.org\/blog\/wp-json\/wp\/v2\/media?parent=763"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.goodmath.org\/blog\/wp-json\/wp\/v2\/categories?post=763"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.goodmath.org\/blog\/wp-json\/wp\/v2\/tags?post=763"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}