This is absolutely nothing like the asteroid example, where knowing that anybody is going to fall victim to it would itself be news of astronomical proportions. Previously there was a high chance the event wouldn't happen, and now it seems likely it will, so that entirely change the calculus of your priorities.

This just completely destroys the analogy. (There are other reasons it doesn't fit too, but one is enough.)

> If astronomers announced that a large asteroid might strike Earth in twenty years, and that we currently had no way to deflect it, nobody would respond by saying, “Come back when you already have the rocket.”

I don’t think the analogy fits, for a couple reasons.

1. People not wanting to know whether they have Alzheimer’s is because of the fear of a fate worse than death — living with Alzheimer’s.

2. People not wanting to know whether they have Alzheimer’s is not the same was not wanting a way to detect it. As you said, being able to measure it may help lead to a cure/treatment. I doubt people are against improving detection — they may just not want the detection to be applied personally.

That's not what would happen. We wouldn't mobilize. We'd fragment. Within days, the prediction would be declared partisan. One bloc would call it settled science; another would call it statistical hysteria. Billionaires would quietly commission private shelters while publicly funding studies questioning whether the asteroid even qualified as "large." News panels would debate whether the projected impact zone was being unfairly politicized. Conspiracy channels would insist the asteroid was fabricated to justify global governance. Others would insist the real asteroid was being hidden. Amateur analysts would flood the internet with homemade trajectory charts proving the professionals wrong. Death threats would arrive in astronomers' inboxes faster than research grants.

Imagine you're born and you eventually learn that there's an asteroid on a collision course with earth, from way before you were born. It's going to take many years to get here and you may die before it hits and so far no scientists have been able to come up with a way to deflect it. Do you care?

Adding newness to the situation makes it wildly different.

People can be fine with being tested so that epidemiologists can work on growing our knowledge and, at the same time, not wanting to know their own diagnosis.

It's also better for people around the Alzheimer's patient, as it will let them understand why someone's personality and behaviours may be changing, and possibly let them be bit more forgiving of such changes. It will also give family more time to plan and understand the health and community services and support are offered wherever they live.

My grandfather had a "fall" at work, he then left that job, and held down 2 more engineering jobs before he was diagnosed with a stroking condition and subsequent dementia. I got the distinct impression he thought he had more time, but rapidly declined.

If he knew he was short of time before his rapid decline he probably would have done things differently. Like not buying a house he would later have to sell to pay for aged care.

If he knew he was at risk of a workplace accident he probably wouldn't have worked as an after hours safety engineer at a major treatment plant, where if the worst had happened he could have endangered others.

(There's enough info in the supplemental link on this page to have an LLM do the Bayes math for you.)

At a personal level, I've been through this with my grandfather.

I want to know. My family wants to know. I want to prepare because there are things I want to do today that I know I won't be able to do in the future.

In many ways, it's just like many terminal cancer diagnoses. You're going to lose that person, but you have some time.

These patients are already seeing doctors. Would you rather your doctor to hide the diagnosis just because your disease isn't curable (for now)? It's not like we're testing the whole population in masse.

Getting an accurate diagnosis is always important. Cognitive decline could be caused by other problems, some of which are more treatable than others.

If this test came back negative it would suggest extra testing to rule out other conditions like a brain tumor or hydrocephalus.

It is frankly shocking to think disease diagnosis would be a useless thing

https://www.alzheimers.org.uk/news/2025-11-18/promising-rese...

There's Lecanemab and Donanemab. The effects are modest however.

The test is optional. Feel free to skip it.

Tell 50 million people they’re likely to have Alzheimer’s then tell them where to donate towards a cure, or treatments to slow it by a decade.

Even though it cannot be reversed or eradicated (yet, let's hope) detection can allow individuals to adopt interventions that help either adjust their lives to better cope with its progression or help mitigate some of the detrimental behavioral consequences. In addition, if you have family to care for it may be impetus to get certain things in order for them before later stages of the disease, etc. It's horrible and bleak, but I could certainly see why one might want to know.

In the lucky case, it can also relieve anxiety. Even though false negatives may still be possible, receiving a negative detection might give people who have anxiety about certain symptoms relief, since they can rule out (rightly or wrongly) a pretty severe disease.

Basically, almost everybody doesn't have Alzheimers. Sampling from the general population you can get better than 94.5% accuracy just by returning negative on every test. You have to know sensitivity and specificity separately to make any informed judgement ... which they try extremely hard not to tell you.

Even without this method, the doctors have been able to give diagnosis with 75.5% accuracy (according to the paper's claim).

I.e. it needs the original 75% accuracy or so and boosts it another 20%.

The problem is that the assessment itself is slow, expensive and requires skill.

What we really want from a test is high specificity (a positive test means you have accuracy) and high sensitivity (if you get a negative test you don't have it).

This is how we can offer screening.

No it's not, that's a reported mean, presumably with the right number of significant digits.

If you want to criticize the variance/stddev, do so, but you picked the wrong metric if that's what you wanted to complain about.

It's used to refine clinical diagnosis after patients present with cognitive severe decline.

By the time someone gets this test, they have severe problems. The purpose of this test is to assist with the right diagnosis.

It's not terrible. This is a relatively good number. Diagnostics is just terribly difficult.

Spoilers: It's anywhere between 1-15 and 5-30% for false positives and 1-15/5-40 for false negatives. That's imaging, biomarkers, cancer screenings, etc

Like, where do you think the concept of "second opinions" came from? Whimsy? Lets go ask a second doctor if I actually have cancer, it'll be fun!

This statement is quite broad and misses several important factors.

First of all, a test's sensitivity and specificity. The math in your example assumes a balanced test, but on what basis? The math comes out quite different for high-sensitivity or high-specificity tests. (Unfortunately, I could not find the numbers for the test in the linked article.)

Secondly, whom are we testing? The prevalence rate in your example (1%) is unrealistically low even for the general population. But would we screen the general population? No, we'd screen high-risk groups: the elderly, those with certain APOE genotypes etc. Predictive values of a test depend hugely on the prevalence rate.

Lastly, it depends on how the results are used. If it's a high-sensitivity test used to decide whom to send to the next tier in a multi-tier diagnostic system, it could actually be quite effective at that (very rarely missing the disease while greatly reducing the need for more expensive or more invasive testing).