Anyway, getting back to that Swedish insurance records study showing that unspayed female dogs (Yorkies included) have a significantly increased chance of developing mammary tumors and pyometra...
Here is a study that validates the methodology used in that study:
Scopus - Cookies Disabled <--This link has the abstract.
A. Egenvall, B.N. Bonnett, P. Olson, A. Hedhammar
Validation of computerized Swedish dog and cat insurance data against veterinary practice records
Prev. Vet. Med., 36 (1998), pp. 51–65
The link I gave should have the abstract.
Evidently the methodology used is widely accepted by the veterinary community, because I came across a 2015 study analyzing Japanese insurance records:
Breed, gender and age pattern of diagnosis for veterinary care in insured dogs in Japan during fiscal year 2010 Breed, gender and age pattern of diagnosis for veterinary care in insured dogs in Japan during fiscal year 2010.
Mai Inouea, A. Hasegawab, Y. Hosoic, K. Sugiurad Preventive Veterinary Medicine, In press.
This latter study included 10,622 Yorkies, and found that Yorkies were in the top 5 breeds at risk for the following major categories of illness: Digestive, Musculoskeletal, Dental, Hepatobiliary and pancreatic, and Neuromuscular. Hepatobiliary and pancreatic is especially interesting, since many Yorkietalk dogs have had liver and pancreas problems. The dogs at greater risk than Yorkies for liver and pancreas problems are: Maltese, Miniature Schnauzer, and Papillon. Pomeranian come next after Yorkies. These data are consistent with what we already know about Yorkies, both anecdotally, and from other kinds of studies.
I've sent PDF's of both articles to Gail (Gemy).