[tedks]

...well, quite a lot actually, because 20 year olds are more like other humans than different.

Humans don't have life stages. We don't wrap ourselves in cocoons and change from grubs into butterflies from ages 16-20. For most of human existence, 20-25 year olds were the substantial power holders.

There's a branch of psychology called developmental psychology. It has to do with how humans change over time. If developmental psychologists only studied undergraduates, we wouldn't have a good grasp of the area, but they don't. It's pretty easy to get kids and elderly people to study. It's even pretty easy to get adults to study. It's more expensive than undergraduates, but it's doable.

Beyond that, what sort of differences do you expect to see in areas like, say, input attention, working memory, fluid intelligence, social behavior, perception, motor control, etc.? 18-22 year olds are pretty much normal adults in all of those regards.

The thing that makes this really insignificant is that we know so little about how minds work. Psychology has only really existed since Skinner and behaviorism made it a real science. If I spent 10 seconds I could think of nice, clever-sounding retorts as to why the perception system of a 22 year old is vastly different from the perception system of a 32 year old, but in reality we know almost nothing and learning anything is good. As Heinlein said, it's wrong to think the world is a sphere, but it's much better than thinking the world is flat.

These discussions about replication always sadden me, because they miss the point by so much. Psychology is one of the least respected and yet most vital sciences. The problem is that everyone is a lay expert, because everyone has a mind and thinks they understand how minds work. Psychology has taught us so many valuable, horrible and beautiful things about ourselves.

If you're reasonably intelligent, you can come up with reasons not to believe anything. It's easy to discredit things. It's hard to build things.

(It's also false that psychology studies are only performed on undergrads, usually undergrads are a good pilot testing base and then you move on to externally recruited populations, unless there's really no reason to do so based on the field.)

[couchand]

If you're reasonably intelligent, you can come up with reasons not to believe anything. It's easy to discredit things. It's hard to build things.

This comment is remarkably troubling to me. There is intrinsic value in replication studies. Showing that an effect does not exist or is far weaker than (or, alternatively, exists and is just as strong as) initially reported is just as much "building" our understanding of scientific truth.

No, scratch that, it is far more important than the original study. The original is more like a sketch, and as the results are confirmed or disconfirmed over the course of many subsequent studies the solid building takes its true form.

These discussions about replication always sadden me, because far too many researchers miss the point of the scientific method.

[tedks]

...you're responding to a point I didn't make. That comment is about the fallacy of psychology "testing everything on undergrads."

Please read what you respond to.

[couchand]

I apologize if I misrepresented your point. I went back and re-read your comment again, and I guess I'm still confused. It looks like you pivot in the middle of your comment with the statement: These discussions about replication always sadden me...

What did you mean by you can come up with reasons not to believe anything regarding testing on undergrads? That sounds to me like a broader complaint about replication generally.

How is it that discussions about replication "miss the point"? I thought the point was that replication is fundamental to science, so it seems like these discussions are usually spot on.

[pacaro]

This may be a "get off my lawn" comment, but my understanding is that pediatric psychiatrists and psychologists will treat patients up to 25 years old. The boundary between childhood and adulthood is labile and varies from person to person. From my own experience, re-reading books like "100 years of solitude" or "the unbearable lightness of being" at ten year intervals shows me how much I have changed

[tedks]

...but the optic nerve of a 20 year old is the same from a scientific perspective in almost all respects to the optic nerve of a 30 year old. Maybe if that optic nerve signaled some horribly deep work of literature like 100 years of solitude, the older brain behind it would interpret it differently, but that nerve is the same.

When you remember the amazing swelling feelings of being ~adult~ you had when you last read 100 years of solitude, your semantic and episodic memory systems are, functionally, identical to what they were when you read it the first time. Maybe your fluid intelligence is a little less fluid, but that doesn't really start until you've aged a lot.

I'm sure you've changed as a person. I'm sure you have a wealth of new experiences and are entirely different from your past self. This is irrelevant to the physics, chemistry, and psychology of your body.

[pacaro]

In general I agree with you. It is important to separate experience from capability (there's probably a better word here).

Much of the social psychology may not fit easily into that division though. To pick on a common whipping boy in these arguments, Milgram's obedience study, what is the role of experience in any set of choices like those given to the participants. The asymmetric responsibilities when there is a power dynamic is something that some people learn somewhere along the line.

I'm rambling a little but I feel that some of the observed effects in these experiments may be things for which experience may provide a learned immunity

[tedks]

Milgram's obedience study was tested on adult men, between ages 30-40 IIRC. There were 19 later experiments, you wouldn't call them replications because they weren't exactly the same, but they were all consistent, and they sampled diverse (for the 50's) populations.

If you didn't know that, and were assuming it was tested on undergrads exclusively, you should recognize that your assumption was wrong, and propagate that through your belief graph.

[DanBC]

I agree that human brains co tinue to develop through the 20s.

In the UK CAMHS or CYPS (Child and adolescant mental health services or children and youn people services) have a hard cutoff at 18.

Someone who is 17 years 11 months old will be placed into a CYPS team and a CYPS in patient unit if needed, and someone who is 18 years and 1 day old will go to an adult team and adult inpatient units.

There are considerble problems at the moment with:

Transitioning from CYPS to adult services

Having enough inpatient beds for young people.

Young people either have to travel hundreds of miles to get a bed or they have to go into an adult unit. That's a serious breach of commissioning and regulators get involved.

[watwut]

Except that generations differ from each other in both behaviour and values. Moreover cultures differ from each other in both behavior and values.

When you make a test on American 18-20 years old, you may be learning something universal about humans or you may be learning something special about products of current American educational system. Perception and social behavior of current American 18-20 may seem universal to someone who is American 18-20 or close to them, but not necessary when you come from different culture.

Many of those studies try to measure how much you are influenced by something you read/heard ten minutes ago, how much likely you are to cooperate/compete in some special situation etc. Are you claiming that these reactions are necessary universal?

[scott_s]

We don't have discrete life stages like butterflies, but my understanding of developmental psychology is that we very much do have mental-ability life stages. Part of that understanding is that we don't fully mentally mature until around 25. If that is true, then it does call into question using mostly 20-year-olds to conduct psychology experiments.