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Survival probability models for male neutered (A) and female spayed (B) Shih Tzus. Middle lines depict the probability of survival for a dog at 7.5 years age in 2003 (assuming survival to at least 9.5 years), with the upper and lower lines depicting 99.79% confidence intervals. The survival of dogs in the normal body condition group is shown in red, whereas that of the overweight group is show in blue
