I've seen several people who were trying Woopra in a side-by-side comparison on their site with another "live" analytics provider asking the question, "Why do the LIVE visitor numbers differ?"
I've also seen a couple of blog posts where astute webmasters picked up on the fact that the other companies numbers are wildly inaccurate. Let me take a moment to explain why Woopra's method of determining a live visitor is absolutely the most accurate in the industry.
Continuous Updates Count!
When we first built Woopra (and I mean way, way back before anyone had ever heard of it) we put a basic system in place which notified us when a visitor was on the site. It used an "average" visit time to estimate how many visitors remained on the site at any given time.
This is the method most similar to other providers who claim to have "Live Web analytics". But we quickly came to realize that these were not truly "live" visitors. They were just single blips in time, between which we were waiting for people to hit another page before we knew for sure they were still around.
We scrapped that method, because it sucks. Instead, we implemented a far more robust, and far more costly, system in which the Woopra script calls back to our servers in the data center every few seconds to basically say, "I'm still here".
Notice in the image above, which is a screen capture taken of the Firefox extension Firebug, that only Woopra keeps updating our servers about the status of the visitor on the website. So, why does any other service provider claim to be Live? They aren't.
By the way, for those of you who don't know, you can use Firebug to see how quickly different elements of your page load. You can see from the results in this image that Woopra is very fast and in no way impacts page load times.
The Only Truly Live Web Analytics
What this means is that when you are looking at Woopra and you see a number of people being reported as LIVE, they have all called back to the server with an update within the last few seconds.
In fact, we monitor nearly HALF A BILLION requests per day. Yeah. Ridiculous, huh? Twitter doesn't see that volume of daily requests.
Hence, The Differentiation
So, when Woopra tells you that there are 100 visitors on your site, that means that 100 visitors are pinging the Woopra server about 1,000 times a minute. And this explains why exactly zero of our competitors do it this way. It's extremely costly.
UPDATE: Check the comments... I learned that Chartbeat DOES have a somewhat similar implementation that pings back to their server. They call an image, not a script... but they DO get live updates! Yeah!
But hey, for YOU, we are willing to do it! Besides, if we did it any other way, you wouldn't be able to actually have that useful live chat feature built into Woopra.
So, the next time you compare Woopra's LIVE number to anyone else, now you know which one to believe.