Looks like November wasn't a great month for posting, for me. Well, I'm back, and this time with another medical term. As with the others, if a medical doctor reads this and I'm wrong about something, I would love to hear about it so I can fix it. I am writing from a non-medical person's perspective for other non-medically trained people, but I hope I'm not making any doctors cringe.
So this time it's "longitudinal study". The basic idea behind a longitudinal study is that the study follows specific people for a long time—years, or decades. These can be used to tease out things like what affects aging or why some kids develop asthma but others don't, and many more.
Unlike a double-blind study, a longitudinal study doesn't always know what it's looking for, exactly, when it starts. They'll often have a goal, such as the aging or asthma studies I linked above, but they don't always know what the cause is that leads to the effect they're studying, and that's what they're trying to find. A double-blind study is the opposite: testing a cause to see what the effect is.
It's one of those things that really doesn't translate to the type of chemistry that I do, because with humans, and especially with long-term health effects, cause and effect is very much not immediately obvious. Chemistry is pretty simple in comparison: you mix stuff together and something happens, and if you mix the same amounts of the same stuff together, the same something happens—usually pretty quickly.
Stuff like cancer shows up decades after the dose of carcinogen, though. And that's the sort of thing that only a longitudinal study can capture with any kind of accuracy, by asking and testing what people do now, and in ten years, and in thirty years, and finding out what illness they come down with, or die from.
So they could look at some longitudinal study data and ask, ok, these people died of this disease, and these people didn't. What's different about these groups? But because there are so few simple cause and effect relationships in human health, you end up with percentages. People with this characteristic are 10% more likely to end up with this disease 30 years later, or whatever.
It can be frustratingly vague, especially when there are people who want to be healthy and do everything "right" and still get sick, and there are people who do everything "wrong" and live to be a hearty 100 years old. Despite them, those trends and percentages still hold. Trends and percentages don't say exactly what one person is going to experience. And for now, it's what we have.
Also, I'm signed up for a longitudinal study! I hope my blood samples and questionnaires help doctors figure something out, 20, 30, 40 years in the future, so I'm going to make sure I stay in the study for future questionnaires and samples that they need to track me over time. I'm signed up for one that is intended to be used by studies thought of in the future for what lifestyle and environmental factors affect what diseases, and provide a nice long dataset for those future researchers who want to investigate stuff like a chemical exposure connection to disease (I want to know this—I want my chemical facilities to be safe and not make people sick) or a lifestyle connection to diseased or healthy outcomes.