Scientific principles play out in real life, sometimes without you even realizing it.
One of my cats has been pretty ill for a few weeks now. She had a vomiting episode, and then just pretty much stopped eating. She's always had what I would call a "sensitive tummy" but has otherwise been pretty healthy. So I was convinced that she was a likely victim of inflammatory bowel disease (IBD) and that it had finally caught up to her.
When she stopped eating, we took her to the vet immediately, where she was given an anti-nausea medication and some fluids. We scheduled a "GI Panel" - a special blood test that looks at the functions of the pancreas and tests vitamin levels to look at overall digestive functioning. Abnormal results can often be an indicator of IBD or other health problems that might lead to loss of appetite such as B-12 deficiency or pancreatitis. Her bloodwork came back "boringly normal" but the symptoms remained. It got to the point that all she would it was small amounts of chicken baby food. The vet recommended an ultrasound to look for other signs of inflammation of the intestines, which we scheduled as soon as we could.
The ultrasound showed some thickening of the intestines, which can be an indicator of IBD. Bingo! Unfortunately, the only way to know for sure is to biopsy the intestines; cancer can be another closely related problem of the intestinal system, and it doesn't always show up on a U/S. But convinced that the U/S told us what we needed to know, I opted for immediate treatment of IBD symptoms, in hopes of getting her some quick relief. A $2500 invasive surgical procedure on a sick cat also wasn't sounding too good to me at that moment.
She was on fluids, an appetite stimulant, anti-nausea medication, b-12 injections, steroids, pepcid and antibiotics. Yet she wasn't feeling any better. She was still lethargic and barely eating. We took her for an emergency visit when suddenly her abdomen looked swollen. She was brought to an internal medicine specialist who did another ultrasound and x-rays which led to a completely new diagnosis: nine days later we discovered it was not inflammatory bowel disease, but heart failure.
How did her diagnosis go so wrong? I blame it partly on confirmation bias, the tendency to interpret information in a way that confirms one's preconceptions. It might mean weighting evidence that supports your hypothesis more heavily than the situation actually merits, while ignoring other evidence. This process is often unconscious, and can be driven by motivation (e.g. to get a quick answer about what is wrong with your cat), such as seeking information that confirms one's beliefs. This can lead to ignoring information that doesn't agree with your hypothesis, seeing patterns where they do not really exist, or only looking for things that confirm your beliefs. From that point, future information seeking may also be biased, leading you down a completely wrong path, be it more scientific or just cat-illness chasing.
Without getting into too much Bayesian statistics, the problem stems from, for example, only looking at the likelihood of seeing lethargy and lack of appetite if your cat has IBD, instead of also looking at the likelihood of seeing those symptoms if your cat does NOT have IBD. The ratio between these two probabilities is what tells you how likely your hypothesis actually is.
Unfortunately, the treatments for IBD (especially prednisolone and fluids) are contraindicated in the case of heart problems, and may have tipped the scale against my kitty's favor. Luckily, she is currently stable, we now have a correct diagnosis and she is on medications to take the pressure off the heart. Sadly, the diagnosis is a pretty serious one, with a guarded prognosis; we'll know more once she sees a cardiologist. My cat is going to have a heart doctor!
It was an important lesson learned that applies to all aspects of decision-making. It is a good idea to always weigh multiple possibilities, and try to get dissenting opinions. Ask what other explanations there could be for the evidence you are seeing. Constantly reweigh the information (especially if the results don't fit). Not getting locked into an answer immediately could in some cases, be a matter of your cat's life or death.