Yesterday, we talked about the placebo effect and the ways in which it might affect a pet’s response to treatment. I also mentioned interesting research that looked into how caretakers’ perceptions can be altered by the assumption that treatment will be effective. Let’s look at that study in more detail.

Fifty-eight dogs that were enrolled in the placebo arm of a clinical trial for a nonsteroidal anti-inflammatory were included. According to the study, owners and veterinarians were not aware of which dogs were receiving the drug and which were receiving a pill that was identical in all other ways except for lacking the active ingredient.

The gold standard against which the owners’ and veterinarians’ evaluations were measured was a force platform gait analysis. Essentially, this is a sensor that determines how much weight a dog is bearing on a limb when he steps on it. A dog’s lameness was considered to be better if its ground reaction force increased by 5% or more of its body weight and worse if it decreased by the same amount. Otherwise, the lameness was classified as being unchanged.

Dogs were reassessed every two weeks for a total of six weeks. Each time, the dogs underwent three evaluations:

1. Force platform gait analysis.


2. Owners completed a questionnaire evaluating their dog’s lameness as greatly improved, somewhat improved, appeared unchanged, or appeared worse.


3. Board-certified surgeons evaluated each dog’s posture, lameness at a walk and trot, willingness to raise the leg on the opposite side of the body from the painful one, and signs of pain during manipulation of the limb.

Researchers identified the caregiver placebo effect as occurring when owners or veterinarians thought the dogs had improved when they hadn’t or thought they were unchanged when they were actually worse. The study revealed:

The caregiver placebo effect for dogs with osteoarthritis appears to be approximately 57% for owners and 40% to 45% for veterinarians when they are questioned (owners) or visually evaluate (veterinarians) a dog's lameness. This caregiver placebo effect was enhanced [got worse] with time.

The researchers also cautioned:

The data of the present study arguably underestimate the caregiver placebo effect for owners and veterinarians, considering that caregivers did not have to match limb function exactly and were aware of the fact that 50% of all dogs would be in a placebo-treated group. Another potential contribution to our data being an underestimate of the caregiver placebo effect for owners is that owners received a financial incentive ($500) to participate in this study. If they had actually paid for a treatment, it is possible they could have experienced cognitive dissonance. Cognitive dissonance is an uncomfortable feeling caused by holding 2 contradictory ideas simultaneously. People try to reduce this disagreement in their mind by justifying or rationalizing their attitudes, beliefs, and behaviors. This could occur if an owner had to pay for a treatment and was told that the treatment would be effective. The owner may believe their dog should get better and ultimately dismiss evidence that the treatment was ineffective or not as effective as they had believed.

The problem with the caregiver placebo effect (in addition to complicating the evaluation of scientific research) is that it results in pets receiving inadequate relief from their symptoms. Owners can help guard against this by identifying objective measurements of their pet’s well-being (e.g., the frequency and duration of seizures, the time it takes for a dog to climb the stairs or walk around the block, the number of times a cat "misses" the litter box in a week) and recording what they observe in a health diary.

It’s much harder to paint a rosy picture of what’s going on when the facts stare back at you from the page in stark black and white.

Dr. Jennifer Coates

Image: Susan Schmitz / via Shutterstock