The problem here is that due to the base rate fallacy, accuracy percentages for medical tests are widely misinterpreted, so a "90% accurate" disease-screening toilet is a recipe for lots of unnecessary procedures and emotional trauma. Even at 99%, a positive hit for most diseases is still probably a false positive.
That entirely depends what the outcome of a positive screening result is. Screening doesn't really care about the base rate —and yes, if you were going to start chopping bits off immediately, it would matter— it's just there to weed out the negatives.
Doctors currently manually screen for many cancers, over entire demographics. It takes up an extraordinary amount of time, takes decades of training, and still misses cancer.
A breathalyser or toilet can sample you twice a day. That can feed into a risk analysis that pushes you onto blood screening (again, largely automated chem detection, only nursing support required). If you're still setting off alarms at that point, you go to the specialist.
And that's the point. Whereas they'd have been seeing 100% of their demographic, these machines are doing layers of screening for them. They end up only seeing a tiny fraction, where their job shifts to final confirmation and treatment.
What is really important is these machines cannot miss things. A low false positive rate is acceptable. False negatives over zero cannot be allowed because they'll delay or prevent further testing.
> A breathalyser or toilet can sample you twice a day. That can feed into a risk analysis that pushes you onto blood screening (again, largely automated chem detection, only nursing support required). If you're still setting off alarms at that point, you go to the specialist.
The long term, personalised health view behind this is what's interesting to me.
Medicine has a lot of wide-windows of what's normal for "people", but often the first signs of an underlying issue is that something that was normal for you at one end of a window begins to move, or change, in ways it hasn't before.
One sample of a blood test might tell you "that level is a little lower than average, but still not low enough we'd worry". But the historical knowledge that "I've actually always tended to be on the higher side of average for that measurement" changes the picture drastically.
Like you say, when it comes to looking at false positives of new tools like this, sure, a tool may be useless at giving you a one time 100% accurate reading, but if you can watch the trend of it over time that may be valuable.
It might even be a good thing. With enough regular feedback, we might emotionally adjust to the realization that "maybe you should get checked out" is not OMG I'm going to die.
There is a huge misconception about the value of screening in the general population. It doesn't do what most people think it does. Even with emotional adjustment it is entirely unclear that screening for things like cancer is ever good for the patient. Look at work by the oncologist Vinay Prasad: https://www.bmj.com/content/352/bmj.h6080
a) It's just not that easy to "everybody needs to adjust" -- people are different wrt. what causes anxiety, etc. It seems a priory quite plausbile that there's a significant genetic component to this.
b) "Get checked" may itself cause problems, for example: Scans for breast cancer involve radiation which may actually cause cancer. Biopsies can also be quite invasive. Obviously the risk is low, but depending on the exact numbers and it might actually be better to not get screened until one is in a known high-risk group (where the base rate fallacy doesn't skew the results so much).
And if it was massively affordable, portable, etc.
(On a lighter note I just can't help but think of a few scenes from a particular movie when we approach new automation fields... "This one goes in your mouth, this one goes in your ear, this one goes in your butt. No wait...")
Imagine if your toilet said, "uh hey so your X levels seem unusual. This might be nothing but you should seek a doctor"