I'm in the process of analyzing our website to determine where we're losing customers. I want to find out how many are lost before the page even finishes loading.
What is this metric called? And how do I gather it for my website? And are there any services that offer this (Google Analytics I'm looking in your direction...)?
You are probably looking for the Bounce value in Google Analytics. This counts the pages that people click on then do not stay around to read. I am not sure if it measures whether the page completes or not.
Actually from the help:
Bounce rate is the percentage of single-page visits or visits in which the person left your site from the entrance (landing) page.
So it does not measure if the page is not completely loaded, only if the visitor does not continue using the site. So this may be not what you are looking for.
Depending on the technology you use, you can log this in the server-side. Using ASP.NET you could use the HttpResponse.IsClientConnected Property at the bottom of your page and then log to your database if it's false.
Another alternative would be to log all requests to your page with a column (loaded) with an initial value of "0". Then, when a 1x1 image on the page is loaded, update the request-record to "1".
Assuming you have a reasonable level of granularity on your web server logs (i.e. the first request, and the completion of the page) you should be able to knock together some stats from parsing your log files.....
Of course, I'm sure there are some tools to do that around, but if you feel the need for a bit of coding exercise......
;)