Alexa Toolbar and the Problem of Experiment Design


	Alexa Toolbar and the Problem of Experiment Design

noahwesley

3-10-2007 12:08 PM

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tags:

siteping

1 Comment |

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3-10-2007 2:29 PM

egoldstein

I can tell you from our experience with clipmarks that Alexa's numbers seem totally off. Our traffic today is double what it was at the start of the year, yet our chart on alexa barely shows any growth.

Would be interesting to see what would happen if everyone who frequents this site decided to install the Alexa toolbar on the same day

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<div style="margin: 12px 0px; font-family: arial; color: #333333; background: #ffffff; border: solid 4px #e5e5e5; width: 100%; clear: left;"><div class="CM_CTB_Content_Wrap" style="margin: 0px; padding: 0px;background-color: #ffffff;"><div style="border-bottom: solid 1px #dcdcdc; white-space: nowrap; margin-bottom: 8px; background-color: #eeeeee ;background-image: url(http://clipmarks.com/images/source-bg.gif); background-repeat: repeat-x; height: 24px; line-height: 24px; vertical-align: middle; padding-bottom: 4px; color: #666666; font-size: 10px;" ><a href="http://clipmarks.com/clip-to-blog/" title="see clips that are hot right now"><img src="http://content.clipmarks.com/blog_embed/8c4ec9e6-9946-4e53-b146-2b8b7d7112d8/EA7DFC83-B206-431F-8A7A-1B0E80BE7519/" alt="" width="19" height="19" border="0" style="vertical-align: middle; margin: 0px 4px; display: inline; border: none; float:none;" /></a>clipped from <a title="http://norvig.com/logs-alexa.html" href="http://norvig.com/logs-alexa.html" style="font-size: 11px;">norvig.com</a></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://norvig.com/logs-alexa.html"><H1>Alexa Toolbar and the Problem of Experiment Design</H1></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://norvig.com/logs-alexa.html"><P>
Despite these caveats, the difference in the stats is quite profound.
For example, I get about twice the pageviews of <A href="http://mattcutts.com">mattcutts.com</A>, but his Alexa pageview
ranking is about 25 times more than mine (I got this by looking at the
1 year, most highly smoothed graph on Alexa, and then squinting to
guess at the mean, so that's yet another source of error in my study.)
What that means is that people with the Alexa toolbar installed are 25
times more likely to view a page on Matt's site versus mine, but
overall, all users view twice as many pages on my site.  That's a 50
to 1 difference introduced by the selection bias of Alexa.  
Presumably this is because Matt's site
is really appealing to a core group of SEO enthusiasts, many of whom
also like the Alexa toolbar.
</P></blockquote></div><div style="margin: 0px 6px 6px 4px;"><table style="font-size: 11px;border-spacing: 0px;padding: 0px;" cellpadding="0" cellspacing="0" width="100%"><tr><td style="background:transparent;border-width:0px;padding:0px;">&nbsp;</td><td align="right" style="background:transparent;border-width:0px;padding:0px;width:107px" width="107"><a href="http://clipmarks.com/share/EA7DFC83-B206-431F-8A7A-1B0E80BE7519/blog/" title="blog or email this clip"><img src="http://content7.clipmarks.com/images/c2b-foot.png" border="0" alt="blog it" width="107" height="17" style="border-width:0px;padding:0px;margin:0px;" /></a></td></tr></table></div></div>

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