For the Somerville Dog Owners Group's initiative to help the City double the number of dog licenses it issues every year, an enterprising member did some research on how to estimate the number of pet-owning households and pet populations in a community.

Everywhere we go in Somerville we see dogs. Dogs on leash, being walked, pulling toward some adventure only they can smell. Dogs gamboling in the parks, unleashed and disobeying the signs they cannot read. Dogs sniffing, dogs prancing, dogs smiling, and sometimes, but not all that often, dogs barking.

As of today (October 3rd), there are 828 dogs licensed in the city of Somerville, but every dog owner knows that that number is very, very low.¹

So, how many dogs are there in Somerville?

There has never been a census of pet ownership in Somerville. However, the American Veterinary Medical Association did a national census of pet ownership in 2002. Cross-referencing their findings with the US Census of 2000, they have developed formulas for estimating the number of pets in a community.

The national average for households with dogs is 36.1%. These households with dogs also have an average of 1.6 dogs. We can use these numbers to estimate the number of dogs in Somerville based on the national averages.²

According to the US Census of 2000, Somerville has 31,555 households.

31,555 x 0.361 = 11,391 households with dogs

11,391 x 1.6 = 18,226 dogs

Eighteen thousand dogs! Can that possibly be true? Most people with whom I?ve spoken can?t believe a number half that. I have to confess that eighteen thousand dogs seems high to me too.

There are two assumptions about dog ownership which might lower that number. One common assumption is that fewer people own dogs in the city than in the suburbs or rural areas. Somerville being a very dense urban area would, therefore, have fewer dogs than national averages would suggest.

The second assumption is that homeowners own more dogs than do renters. Somerville?s homeownership is just 46% of the national average and the City should, therefore, have fewer dogs.

But these are assumptions that are not backed up by any numbers that I?ve been able to find. We are all aware that there are plenty of dogs in Somerville. The density of our town does not appear to unduly deter dog lovers from their companions. And if the experience of som|dog?s chairperson is any indication, renting is no barrier to dog ownership.³

Let us, however, take these factors into account.

If Somerville?s density discourages dog ownership so much that the city has only half as many dogs as the national average, then:

18,226 x 0.5 = 9113 dogs

If only homeowners in Somerville own dogs, then:

18,226 x 0.46 = 8384 dogs

If only homeowners own dogs and there are only half as many dogs as the national average, then:

18,226 x 0.46 x 0.5 = 4192 dogs

The numbers based on only homeowners owning dogs are clearly based on a fiction which artificially and unreasonably lowers the numbers of dogs. Still, it should be clear from this exercise that there are very many more dogs in Somerville than the 828 currently licensed by the city.

Based on these numbers, I would be surprised if there were fewer than 7,000 dogs in Somerville, but not at all surprised if there were more than 10,000.

. . .

¹ For the past year and a half, members of som|dog have been informally suggesting to dog owners that they license their dogs. We have not been systematic in this by any means, but the city has seen an increase in the number of dogs licensed by nearly one-third. That is a lot of new dogs licensed ? and we keep meeting unlicensed dogs.

² We can simplify this down to one number by multiplying the percentage of households by the number of dogs per household.

0.361 x 1.6 = 0.578

31,555 x 0.578 = 18,239 dogs

The difference between total numbers of dogs here and above is due to the way the decimal points were rounded.

³ There is quite a bit of anecdotal evidence which suggests that a fair number of landlords do not allow dogs in their buildings. However, som|dog has plenty of members who own dogs and rent.