Final answer:
The size of a pet is the least likely characteristic to affect pet health insurance premiums, as other factors such as species, breed, age, and reproductive status are more significant in determining risk and healthcare costs.
Step-by-step explanation:
When examining the characteristics of an animal for which pet health insurance is being purchased, the factor which is LEAST likely to affect the premium of the policy is '5) Size'. Insurance companies generally consider variables like species, breed, age, and reproductive status as they have significant implications on the expected healthcare costs associated with the pet. These factors are closely linked to both the likelihood and costs of potential health issues that may arise. For instance, breed can influence the risk of congenital conditions, age correlates with the likelihood of needing healthcare, and reproductive status can impact costs related to breeding or pregnancy.
However, the size of the pet is generally not as influential on the premiums because health risks and life expectancy are not as directly connected to size as they are to other factors. Actuarially fair insurance rates are set to reflect the risk associated with insuring the animal, and size is considered less predictive of risk compared to breed-specific diseases or age-related conditions.