[LeifCarrotson]

I completely agree that randomized intervention studies have enormous value when compared to observational studies.

In this example, it would be particularly hard to establish a causative relationship that said "hearing aids inhibit dementia" or "hearing loss causes dementia" if instead all you had was a population, some of whom used hearing aids, and some of whom had varying levels of hearing abilities, and some of whom developed dementia. In all the noise, you'd be very fortunate to find that a control group of people with undiagnosed (how would you ever measure that!) hearing loss who failed to get hearing aids had cognitive decline in excess of that experienced by those who did get hearing aids. Here, instead, the intervention is "the coin flip said you're in the hearing aid group/you're in the health education group."

Of course, the murky ethical issue here is that this randomized intervention resulted in some people having poorer hearing, perhaps permanently (use it or lose it!) and some people having more rapid cognitive decline. This randomized intervention directly caused real suffering. Nearly 125 people in the heart-health group with increased risk of dementia onset were assigned to a study that just received health education. For at least three years, they had reduced hearing and a reduced ability to communicate, and after three years, they had significantly greater cognitive decline.

Caution is good, but in general I have no problem personally with the 'shut up and multiply' application of ethics in this case. There are 8 billion people all getting old, and more being born every day who will eventually get older. It's very important as a species to know that hearing aids slow cognitive decline, and if that meant that 119 people were placed at a slightly increased medical risk, 119 divided by 8 billion is a pretty small number, and 7.999999881 billion who are now more likely to get hearing aids and have slower cognitive decline is a lot of positive utility. But it wasn't me or my mom who can no longer hear and who is suffering from dementia, and some will draw a hard line and say that you can't perform studies that will put even a small number of people at increased risk.

We should be careful to evaluate merit and limit harm, but we should perform more randomized intervention studies.

[skybrian]

I largely agree, except that choosing a denominator of 8 billion is really dubious. The number of people for whom this study will result in them getting a hearing aid when they otherwise wouldn't is unknown, but unlikely to be nearly that high.

You can't actually do that math. Or rather, you can but the inputs to your spreadsheet are whatever you made up.

[LeifCarrotson]

Attempting to do the math is better than the alternative of going with your gut. The numerator is also an overestimate, not everyone suffered excessive cognitive decline.

If this was a critical decision (like it was for the authors of the study, unlike it is for the authors of Internet comments) you can work for better inputs.

Most importantly, though, we're trying to understand if that fraction is greater than one or less than one. There's a number that might be 8 billion or might be a tenth or a hundredth of that in the denominator, and a number that's on the order of 100 - or maybe 10x that, or maybe 1/10th that. But it doesn't matter, because it's not close, the ratio is still a million to one.