How do I diagnose as a Doctor?

I've recently started a Sim who is going down the doctor career track, and things were going well until I started having to Diagnose patients myself.

If you perform all the possible examinations, sometimes there is more than one possible diagnosis to choose from, and I couldn't figure out how I was supposed to narrow this down.

Getting the diagnosis, and therefore treatment, wrong give you a big penalty to your work performance, and the requirements for promotion include several successful diagnosis and treatments.

Does my Sim need more of a certain skill to improve their chances of succeeding at tests and analysis? Does their mood effect the chance of failure?

Is there more to this than just performing exams and tests until you have a "Compelling Diagnosis" with only one option?

Solution 1:

It seems that the player is supposed to learn how to recognise the illnesses, rather than the sim itself being able to fully diagnose.

While performing examinations will narrow down the diagnosis options, the player must watch the way the patient emotes, and look out for rashes and marks on the patient. The behaviour and appearance of the patient will tell you which of your Sim's possible diagnoses are correct.

Diseases and Their Symptoms:

• Rashes - These may present with any number of illnesses, so don't think right away it's itchy plumbob. They are meant to be indicators a patient is really sick, so you can rule out 'Not Sick'. Some rashes only present with certain illnesses. There are three types: swirly, orange and green spots, and tiger stripes.
• Sweaty Shivers - May itch, may have fever (shiver), may have orange and green rash.
• Bloaty Head - May have a headache, may have orange and green spots, may have steam coming out of their ears. If they have steam, it's definitely Bloaty Head.
• Starry Eyes - May be dizzy (shows stars around their head), may have a swirly rash, may swat at invisible objects in front of them. If you see them swatting, it is surely starry eyes.
• Llama Flu - May have a fever, may cough/sneeze, may have orange and green spots rash, may have a cloud of gas around them.
• Gas and Giggles - May fart and giggle at random times, may have a tiger-stripe rash, may have stomach ache. Watch their idle animations for lots of laughing. Laughing itself is not necessarily a symptom, but they may appear to do so uncontrollably.
• Triple Threat - May be dizzy, may cough/sneeze, may have swirly rash. Lack of swiping as with Starry Eyes, and lack of fever as with Llama Flu. Requires surgery.
• Itchy Plumbob - May have a tiger stripe rash, may itch. You can tell this apart from Sweaty Shivers by the presence of Tiger Stripes and lack of a Fever.
• Burnin' Belly - Visible stomach pain, may have fever. Requires surgery and is a rare illness - perhaps the most rare of the diseases Doctors can diagnose.

Source: https://www.carls-sims-4-guide.com/careers/gettowork/doctor/