To further add to the difficulties with dog ownership/popularity stats...
Most data comes from kennel clubs.
America has two main ones:
- United Kennel Club, which will register American Pit Bull Terrier
- American Kennel Club, which does not list APBT, but does list the American Staffordshire Terrier, and the AmStaff can be listed with the UKC as an APBT.
Then theres insurance - now many insurance companies will not cover APBT or charge a much higher premium, so of those insured, most won't be described as what they are but as crossbreeds, Lab crosses, AmBull mixes, etc etc. And most won't be insured at all.
Data from rescue kennels - tends to lump AmStaff, AmBull and APBT together as 'pitbull'. if they list them that way at all. Again there is a tendancy to list them as crossbreeds of less controversial breeds like Labradors and indeed there are a lot of Lab x types out there in both the US and UK.
In the UK of course, whilst theres more dogs insured, we're still getting data from the Kennel Clubs puppy registration listings so that obviously will not include crossbreeds or breeds not recognised here. So none of the XL bullies, AmBull, Pitbull type, etc etc.
Insurance companies won't insure pitbull types and as none of those breeds is a recognised breed anyway, those that are insured are insured as crossbreeds. Many will not be insured at all.
The most common breeds in American shelters, are the xl bully/ambull/pitbull types - they make up three of the top four (and jack russell/rat terrier types are number 3).
Unpopular, uncommon breeds do not show up in rescues. People may be ditching them or leaving them to stray, but people are also producing them an owning them in huge numbers in the first place - and I believe this is also evidence that such breeds are more likely to be owned by less responsible owners.