Gav (![[info]](http://l-stat.livejournal.com/img/userinfo.gif){kind=small} blufive) wrote in ![[info]](http://l-stat.livejournal.com/img/community.gif){kind=small} stats_weenie,@ 2005-02-27 11:12:00 |
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| Entry tags: | statsinthenews, websidestory |
Snapshot: WebSideStory and "Firefox gains slowing"
For-pay internet stats outfit WebSideStory have released one of their infrequent "data spotlight" columns, and it's causing some minor waves. This is presumably because Firefox is flavour of the month, and this column is titled "Firefox Gains Slowing". [note: this appears to be a static page with no archive; it seems likely that, at some indeterminate point in the future, the content I am quoting from will be replaced by something completely different]
The growth rate of Firefox’s usage share on the web has slowed in recent months [...] Firefox’s market share grew just 15 percent in the five weeks leading up to Feb. 18, 2005, the latest benchmark available. In the previous six weeks before that, the browser grew at 22 percent clip. These figures compare with a 34 percent increase between Nov. 5 and Dec. 3, which coincides with the release of Firefox Version 1.0 on Nov. 9.
Anyone see the mathematical flaw here? The text above is built on an assumption of steady geometric growth. That assumption is highly suspect - in my experience, [Edit:] no browser's market share has ever grown exponentially no browser with significant usage levels has managed sustained exponential growth in market share [end edit] in recent (Internet time) history. Usage of the internet itself may have done so, in the mid to late 1990s, and that might have dragged the browser du jour up at a similar rate, but after 1998? No chance. I speculated on some possible reasons why back in November. So I did some number crunching. Here are their headline raw numbers:
Browser 18 Feb 05 14 Jan 05 3 Dec 04 5 Nov 04 IE 89.85 90.28 91.80 92.89 Firefox 5.69 4.95 4.06 3.03 "Netscape"* 2.47 2.64 2.83 2.95
[*They've actually labelled the last row "Non-Firefox Netscape and Mozilla browsers". Personally, I think lumping Netscape 4 and Mozilla 1.7 into the same group is fairly braindead, but...]
Unfortunately, the date intervals are irregular - 28, 42 and 35 days. So directly comparing the growth in each interval is pretty bogus in itself (especially with the galumphing great demographic elephant called "Christmas" slap in the middle). Here's the growth numbers I calculated from their data:
Date Interval Usage growth% Growth/day 05 Nov 04 - 3.03 03 Dec 04 28 4.06 34.0 0.037 14 Jan 05 42 4.95 21.9 0.021 18 Feb 05 35 5.69 15.0 0.021
The "growth%" column is obviously what they're quoting in their article. I calculated it using the formula 100x((usage2/usage1)-1). For that number to be "constant" requires geometric growth in usage from one datapoint to the next.
The "growth/day" column is the average growth per day over the preceding interval - calculated with the formula (usage2-usage1)/interval. I think it shows a much more realistic picture (based on these numbers). Namely: after an initial surge in the first interval, growth in Firefox usage slowed, but then stabilised to a linear increase at a lower level. Since the first interval included the Firefox 1.0 release and a huge publicity push, this seems reasonable.
[Update: some extrapolation]
Back in December 2004, it seemed Firefox was a lock to reach 10 percent by mid-2005, ahead of the reported year end goal of the Mozilla Foundation. Given the latest growth rates, the year end target still appears attainable, but a mid-year achievement is unlikely
Assuming continued constant linear growth at the rate seen in the third interval, Firefox will hit 10% in September 2005. Of course, that assumption is almost worthless...
[Disclaimer: this is all based on a grand total of four data points, compiled using unknown methodology from an unknown data set. Guesswork-a-go-go, in statistical terms]
[28-Feb-2005 update: following a prod from David Naylor, WebSideStory have amended their report to more accurately reflect the numbers. Looks more like a mistake than anything deliberate...]
