The problem for us...
With modern web browsers and corporate networks there are now several ways in which tracking information may not get through to your Google Analytics, Facebook or Bing web services. This is not something that you have any control over as it is at the user or corporate end of things that the block is being applied.
Corporate networks and even some home networks can block traffic using DNS or other heuristic blocking algorithms - they simply stop any traffic to the Google Analytics, Facebook and Bing servers effectively meaning the conversions are not tracked.
Users can install add-ons in their web browsers such as AdBlock, Purify, uBlock and many other extensions (list growing by the day) and these remove the tracking components from the page or block their traffic which has the same effect. No tracking back to your service provider for tracking.
If you want to read more on this please reference:
So my stats don't mean anything?
No, they do... The overall effect is that your stats in your tracking service will slightly under report the number of visitors to your pages and the conversions. They are still however extremely valuable to you as they provide demographic, monetary, site path and much much more insight into your visitors. You just need to remember it will be underreporting slightly.
How many people block tracking?
This is very difficult to say but just as an example but currently it is not that high a proportion as far as we can see.
A recent analysis for one of our clients showed out of 148 conversions (as shown in their database) a total of 132 were actually tracked in the tracking service. Not a bad percentage but obviously very contingent on your visitors.