3D Hurts Your Eyes 244
sajjadG writes "After experimenting on 24 adults, a research team at the University of California, Berkeley has determined that viewing content on a stereo 3D display
hurts your eyes and your brain. This can supposedly cause visual discomfort, fatigue, and headaches According to the article, 3D content viewed over a short distance (like with desktops and smartphones) is more visually uncomfortable when the stereo content is placed in front of the screen. In a movie theater, it's the opposite: Stereo content that is placed behind the screen causes more discomfort than scenes that jump out at you. With the explosion of 3D-capable gadgetry such as televisions and mobile phones, understanding just what this kind of technology is doing to our bodies may help us better use it in the future. The only problem is that technology tends to far outpace research, and until we get a better handle on its effects, we're more or less walking blindly into a 3D world."
Get 2D Glasses (Score:5, Informative)
http://www.thinkgeek.com/tshirts-apparel/miscellaneous/e9b4/
Handicapping, Ridiculous, Anti-Progress (Score:5, Funny)
First of all, there's no way to know if two things are separated by a volume of space unless you have a headache. That's how evolution works: the cerebral nerves were caused to evolve specifically by Darwin in order to function as a kind of animal cruelty version of Pavlov's dog in which mapping three-dimensional space actuates the occipital squinting reflex, causing us to narrow our eyes meaningfully at expansive vistas while also wishing for acetylsalicylic acid and a glass of water.
Scientists consider this sort of thing basically self-evident, like the existence of atoms or Jenny McCarthy.
Furthermore, the so-called Disney Cortex is capable of parsing dimensionality exclusively through parallax; in effect, the neck pain caused by this subtle lateral shifting of the head is conveyed via the uvula directly into the cranial brain-case, tapping into the same area of sensitivity exploited by the spatial depth pain discussed above.
Elementary biochemisphology tells us that the only way stereoscopy can function effectively in the real world of fake entertainment is by pulling out all the stop and going holographic, so that the images can be processed and hurt us in as natural a way as possible. This is God's way of telling us that the Holodeck was cool.
Fad researchers have understood this for centuries, since the time the Illuminati first started actively repressing news of the stereoscopic newspaper in 1743.
Your friend in science,
Cheeseburger Brown
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The Disney Cortex? Is that made by evolution specifically to watch Disney movies in 3D?
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First of all, there's no way to know if two things are separated by a volume of space unless you have a headache. That's how evolution works: the cerebral nerves were caused to evolve specifically by Darwin in order to function as a kind of animal cruelty version of Pavlov's dog in which mapping three-dimensional space actuates the occipital squinting reflex, causing us to narrow our eyes meaningfully at expansive vistas while also wishing for acetylsalicylic acid and a glass of water.
Scientists consider this sort of thing basically self-evident, like the existence of atoms or Jenny McCarthy.
Furthermore, the so-called Disney Cortex is capable of parsing dimensionality exclusively through parallax; in effect, the neck pain caused by this subtle lateral shifting of the head is conveyed via the uvula directly into the cranial brain-case, tapping into the same area of sensitivity exploited by the spatial depth pain discussed above.
Elementary biochemisphology tells us that the only way stereoscopy can function effectively in the real world of fake entertainment is by pulling out all the stop and going holographic, so that the images can be processed and hurt us in as natural a way as possible. This is God's way of telling us that the Holodeck was cool.
Fad researchers have understood this for centuries, since the time the Illuminati first started actively repressing news of the stereoscopic newspaper in 1743.
Your friend in science, Cheeseburger Brown
You still believe in Jenny McCarthy?
Everyone knows that's a just a story someone made up to scare children.
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From TFS: "After experimenting on 24 adults, a research team at the University of California, Berkeley has determined that viewing content on a stereo 3D display hurts your eyes and your brain.
I immediately thought of Monty Python. "Shut off that TV, it's bad for your eyes!"
and
"My Brain hurts!"
"Well it will have to come out then."
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It's hard telling what dark hairy orifice they pulled those numbers out of. Buying one makes no sense for the same reason that quadraphonics made no sense in the '70s. With quadraphonics you had to have twice as many amps and speakers (and the speakers are the most expensive part of a good system) and more expensive turntables for a marginal improvement in sound quality. Surround Sound only made it because now they use a "subwoofer" and four cheap speakers, and the price of amplifiers has come down.
With st
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That's how evolution works: the cerebral nerves were caused to evolve specifically by Darwin in order to function
So Darwin not only explained evolution, he also caused it? Wow!
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I prefer to just wear this. [amazon.com] Plus it makes the theater manager uncomfortable!
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Except you'd still see double images. If you want to fix that, you need 2 of those.
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Not if you wear the 3D glasses on top of it, which is obviously what he meant.
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There is no way he meant that - it would be completely ridiculous with only one eye. That's why Toshiba invented this [toshiba.com].
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Hurts the brain? (Score:3, Insightful)
Re:Hurts the brain? (Score:5, Funny)
It's the emotional hurt that kicks in when you realize that odds are high that the movie you're seeing in 3D wasn't actually filmed in 3D and instead was faked so they can rip you off for an extra 5 bucks on your movie ticket.
I think.
Re:Hurts the brain? (Score:4, Funny)
How does this hurt the brain? Isn't it just the eyestrain that gives the headache? I thought the brain itself had no pain receptors.
Mostly it hurts your eye, neck and facial muscles ( a 'tension' headache). Besides, at least for males, the brain clearly has pain receptors. Go kick some guy in the nuts and see what happens.
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Re:Hurts the brain? (Score:5, Insightful)
How does this hurt the brain? Isn't it just the eyestrain that gives the headache? I thought the brain itself had no pain receptors.
Your overly literal reading of the summary hurts my wiener.
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It's not a matter of pain receptors, it's a matter of causing harm. Your brain is accustomed to interpreting two images from your eyes, which are an established distance apart. Movies in 3D do not precisely replicate those parameters, and thus your brain has to compensate, and teach it to handle 3D data under different parameters. Basically, it makes your brain think your eyes aren't in the expected place, and forces it to learn to handle that accordingly. If you watch too much 3D, then I suppose you could
2D hurts your eyes and brain! (Score:2)
And this is true for movies in 2D as well. In a 2D movie, perspective and motion parallax gives the impression that objects are at different distances, yet your eyes have to focus
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It doesn't hurt the brain, nor does it harm the eyes. It's just a headache caused by eyestrain. TFS was simply being sensationalist.
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Hurt: [reference.com] 1. to cause bodily injury to; injure. 2. to cause bodily pain to or in. [...]
You are assuming definition #2. They are using definition #1, which does not imply pain.
Not 3D (Score:5, Insightful)
Re:Not 3D (Score:5, Interesting)
That's because it's not 3D; at best, it's 2½D. The back side of the objects are not projected. There are true 3D projectors that create objects that are viewable from all sides (without special glasses). I call them 3D-in-a-box. You can stand in front of it and see things in 3D while somebody else can stand on the other side of the projector and see the other side of the objects (in 3D).
I wished they stop lying by calling it as 3D but that's not likely to happen. :(
Worse than that, the 'movement' you see on the big screen is just an illusion achieved by displaying still pictures fast enough that the brain is fooled into thinking it is seeing real movement.
And even worse still, I watched a '2D' movie the other day and one object actually moved behind another. That's not 2D. That's not even close.
Sarcasm aside :) I wonder if the 2D stuff we've been watching for the last 100 years or so has any negative effect on the eyes or the brain? Rapidly showing still pictures and showing an image that the brain thinks ought to be 3D but is flat....
Re:Not 3D - Height, Width, Depth (Score:2)
Yes it's 3D, it has 3 dimensions. It's not virtual reality, and doesn't claim to be. You can't wander around it and see it from the back. What you can do is infer the depth based on the stereoscopic effect, just like you can infer height and width based on surrounding objects.
You can't see the back of things, you can't re-focus on something that the camera didn't focus on. Yes it's gimmicky and limited. But there are 3 dimensions, and if you want to count time (as in watching a movie) it has 4.
I think
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By that argument, you can infer depth based on cues present in regular 2-D movies, so should they be called 3D?
You don't need to be able to walk around the movie and view it from the back for it to be true 3D, but in true 3D you woul
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By that argument, you can infer depth based on cues present in regular 2-D movies, so should they be called 3D?
That's called "perspective", and there are various forms of perspective that painters have been using for hundreds of years.
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You are choosing to define 3D as having the ability to change focus, which is not what 3D is trying to be, and it never will be. And yes that's why it confuses a small percentage of people's senses. It's a 3D projection onto a 2D space, but it presents a different view to each eye.
So why do you choose a definition of "true 3D" which requires more than just having 3 dimensions? Why not define 3D as "What you would see if you focus on the same thing the director wanted the focus on"?
Put another way, if you
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Laser holograms are true 3d. I'm holding out until that technology comes around.
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Worse, and the crux of the problem, it's not even a full simulation of 3D from a single forced perspective. They simulate only parallax, but not focal depth.
Especially if it's a Michael Bay movie (Score:5, Funny)
Those are particularly harmful to the brain.
Eyes ... can't ... focus ... everything ... blurry (Score:2)
My brain knows it can't focus, but the instinct is to try and focus. Possible if I viewed enough 3D-like movies, I could overcome that instinctual urge.
Avatar was visually stunning, but I've seen it again at home and
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I am yet to see a 3D movie. I tend to be a bit susceptible to motion sickness, and I can pick up on and be annoyed by a 60-70Hz refresh rate on a CRT that doesn't bother anyone else. And even if none of that is a problem, i'm just as likely to fall prey to the negative placebo effect, going into a movie just knowing it's going to make me feel sick :) I kind of suspect that this is the reason a lot of people have a problem with 3D.
Bring on the class-action suit! (Score:3)
$100 million for the lawyers, free movie tickets for the "class"...
Absolutely terrible title, summary, etc. (Score:2)
Where am I seeing anything about 3D hurting eyes in here? This might just be the worst slashdot heading, summary, and linked article in a while.
The whole study is trying to measure specific angles and distances where 3D is uncomfortable. There's nothing about 3D actually hurting eyes.
The study actually doesn't say that, read it. (Score:5, Informative)
TechCrunch (Along with Ars Techinca and others) got it completely wrong.
http://www.engadget.com/2011/07/22/samsung-studies-3d-viewing-discomfort-finds-out-bloggers-dont/
If you read the study, and not the abstract, you'd know they didn't actually watch any 3D. They tested different situations of focusing on various objects to find out WHY some 3D hurts peoples eyes. They did not "find that 3D hurts your eyes" becuase that's not what they were looknig for.
In fact, they discovered the comfortable range for 3D viewing is wider than previously thought.
But you have to actually read the study to know that. - link to the study: http://www.journalofvision.org/content/11/8/11.full
If you hate 3D, hate 3D, but actually read the article before throwing your two cents in.
--Richard Lawler, Engadget
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So? (Score:2)
i posted a story about this a few months ago (Score:5, Interesting)
http://slashdot.org/submission/1454046/3D-Cinema-Doesnt-Work-And-Never-Will [slashdot.org]
the source of the discomfort is that millions of years of simian and primate eye evolution has created an eye that focuses and converges in parallel
look at a mountain, and your eyes are pointed nearly straight out, and are focused wide
look at a book, and your eyes are slightly cross-eyed, and are focused close in
but, for million of years, this focus and this convergence has always been in parallel. millions of years of our ancestors have never had the need for eyes that, for example, cross in, but focus wide, or point straight, but focus close in. 3D expects our eyes, to, for the first time ever, or, since tens of millions of years ago, take your pick, to work in this unnatural way, unnatural for primates
much like blind cave fish or flightless birds: if the function is not needed, the ability atrophies. of course, BEFORE binocular vision, animals with eyes on either side of their head, for example herbivores and ungulates and certain primitive carnivores, can certainly focus, converge, and even point in independent ways. look at a chameleon: its eyes are pretty much independent entities neurologically and physiologically
but this has not been the case, since before even our distant lemur-like ancestors really started working binocular vision, for our bloodline to have eyes that focus and converge on different tracks. we simply can't do it any more without stress and pain. so this is the source of the discomfort with 3D technology, physically and mentally
there is also some concern that very young eyes, that are still developing, can actually be permanently harmed by 3D
i posted a reply about this a few months ago (Score:2)
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because images moving in rapid succession do not ask our eyes to do anything unnatural to their physiological and neurological design
present day 3D technology (some future tech may solve this problem), by splitting our eyes' naturally parallel efforts of focus and convergence, DOES ask our eyes to do something unnatural to their physiological and neurological design
do you understand now?
anything else i can help you with today?
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http://science.slashdot.org/story/10/06/26/2059205/3D-Displays-May-Be-Hazardous-To-Young-Children [slashdot.org]
fear based hysteria about the unknown is a problem in this world
reasonable concerns based on logic and science is not
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http://www.google.com/search?q=3d+young+children [google.com]
do you work for a 3D company or something?
what is the source of your emotional, factless animosity to logic and reason?
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He's a shill, duh. His homepage redirects you to Engadget.
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"The reasoning against having kids watch 3D content is because their eyes aren't far enough apart yet."
Provide a source, now. Plenty of other animals have great 3D vision with eye spacing CLOSER than that of a human child.
Are you just being purposely obtuse or are you just that retarded?
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There's a reason Sega didn't make a stereoscopic visor set in the 80s, pal. I suggest you actually PAY ATTENTION TO HISTORY instead of simply ignoring it.
Nintendo and Sony ignored Sega's prior attempts at enhanced gaming peripherals, now they're having to put warnings all over their 3D-capable devices.
You really need a new education, the one provided to you is absolute shit.
Isn't the real world 3D? (Score:2)
I had a Ninetendo 3DS for about two months before I realized I couldn't handle the 3D effects. I literally went from feeling buzzed to headache in about 45 minutes.
But the real world is 3D - perhaps the difference is the implementation of trickery, which is why 3D often seems more 'fake' to me than a 2D film.
Sega? (Score:2)
Iirc, researchers working for Sega found something similar related to 3D games and children back in the 80s.
Why Worry? (Score:2)
Strabismus finaly pays off (Score:2)
Come to think of it, the term 3D does not take time into account. 4D would be better. And we can add a couple of Ds for the sound. I tried explaining this to my son. Don't know if he really got it. Anyway, my strabismus finaly pays off
FYI, here's the abstract from TFA (Score:2)
Recent increased usage of stereo displays has been accompanied by public concern about potential adverse effects associated with prolonged viewing of stereo imagery. There are numerous potential sources of adverse effects, but we focused on how vergence–accommodation conflicts in stereo displays affect visual discomfort and fatigue. In one experiment, we examined the effect of viewing distance on discomfort and fatigue. We found that conflicts of a given dioptric value were slightly less comfortable a
No Kidding (Score:2)
This has been "discovered" every time 3D comes around, which seems to be every 20 years or so.
No, it doesn't ... at least not for everyeone. (Score:2)
It's 1760 all over again (Score:2)
When John Baskerville invented a process for making smoother paper, and printed books with the blackest ink and whitest smoothest paper ever seen, Benjamin Franklin said that people would go blind. Others took up this claim, although today almost all books are printed on paper every bit as white and often as smooth, and with inks every bit as black.
But it doesn't hurt very much (Score:2)
This seems to be a very nice, careful study, and the discussion of which conditions are more likely to provoke discomfort is likely to be useful to producers of 3D media. It does not, however, provide a great deal of support for the view that discomfort from this source is likely to be a major obstacle to the popularity of 3D media. For most of the conditions, even when the effect was statistically significant, on the average the subjects ranked the discomfort of the stereoscopic displays only slightly grea
Migraines (Score:2)
They aggravate us with a tendency to get those, which is all i need to know to avoid them.
And yes, i unfortunately did try it with one 3d movie. Never, ever again.
This somewhat makes sense (Score:2)
Perceived distance in stereoscopic imagery is determined by where your eyes cross, if they're not parallel. Infinity is when the parallax, the distance between the position on the left- and right-eye images, is 85mm apart (the distance between your eyes). On a small screen the actual number that represents infinity is going to be smaller, and thus appear at some finite distance between your eyes, and in the movie theater it could potentially be greater than 85mm, meaning... farther than infinity somehow (yo
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I think you a good point on this one.
Peak Oil (Score:3)
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No, he unsuccessfully the verb.
1.21 Gigawatts! (Score:2)
Not without your time-machine, bitch.
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I could have told him that 3D years ago. Besides, that's probably Rority posting again, he has no trouble traveling through time.
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They needed to do an experiment to figure this out? The millions of people that say it constantly wasn't proof enough?
The millions of people were just holding their glasses wrong. Or bringing their car floor-mats to the cinema. Or something else, like intentionally exploding their laptop batteries.
Re:Really? (Score:5, Interesting)
No kidding ... I have seen two movies in 3D, and will never see another. I had eye strain and a headache for several hours after.
I am not paying more to see the movie if it hurts, but, given that everybody else seems to like it, I question how long before I have no option but 3D.
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Since the last few 3D movies have done over half their sales in 2D, I wouldn't be too worried. There's a pretty good 3D backlash building up. If they really start only showing some things in 3D, don't see them at all. Money talks.
Nintendo's learning that with the surprising weakness of the 3DS.
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The only reason I don't have a 3Ds is that when I was looking at it, I didn't have the money in the bank to pay for it. It was pretty mind blowing in terms of what I was seeing. I'm guessing the bigger problem is all those checks the government has been sending to the rich at the expensive of the working classes that's causing that weakness. It's hard to find money for a luxury item when the costs of most things one actually needs are going up in price significantly.
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That, and turning on 3D kills the battery life. Why would I turn on a gimmick when it makes the platform less usable?
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I didn't get headache or anything like that but I couldn't see the movie! I couldn't read subtitles, they were all blurred (luckily I understand spoken English). If the 3D effects was in the middle of the screen I couldn't see them clearly but if they were on the sides I could make something out of them. So I missed half of the movie (Thor) and have to go see it in old fashion 2D. Glasses were working fine and my date sitting next to me could see the movie just fine so it must be something with my eyes. If
Re:Really? (Score:4, Interesting)
I have seen two movies in 3D, and will never see another. I had eye strain and a headache for several hours after
I've seen a few of them myself, because for some reason I kept going back thinking that I might like it on a better movie... or something like that. After seeing Avatar, I won't go back to another 3D showing but not because it gives me a headache or makes me uncomfortable (though it does, to an extent), but because the false focusing and perspective cause me to miss things.
It's one thing to watch a film: you stare at the screen for two or three hours straight, letting your eyes and ears get lost in the sights and sounds while your brain works on understanding the characters and the story. With 3D, I inadvertently spend so much time thinking about what I'm supposed to be looking at that I miss visual or plot elements.
Just my two cents, of course.
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I haven't read TFA yet, but the headaches are easily explained. Stereoscopy isn't the only thing that makes 3D. Besides stereoscopy and various forms of perspective, the eye's focusing distance tells the brain how far away something is as well. So you have your eyes' focus telling your brain an object is six feet away (the distance to your TV set) while the stereoscopy tells your brain it's two or fifteen feet away. That causes the focusing muscles to fight the eye positioning muscles.
You won't have that pr
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I just RTFA, it says nothing about hurting your brain. Phew!
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The two 3D movies I saw didn't cause me any stress, but I just don't see the big deal. The 3D seems muddled and artificial to me. Like trying to show someone a nice painting by either carefully illuminating it on a wall, or setting it on fire and bashing them in the face with it.
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TFA doesn't say there's damage to your vision or brain. You're out the price of an aspirin and a movie, hardly anything to sue over.
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If you clicked through TFA and read the actual abstract, you'd find that they found that stuff behind the screen with the screen at distance was more likely to cause discomfort, and stuff coming out of the screen with the screen at a short distance also more likely.
It also went on to discover that the necessity for refractive correction in a person's eye's was a good predictor of whether someone feels discomfort.
So if you're getting a headache, your eyes are probably a lot less than perfect already.
Yes they
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If you clicked through TFA and read the actual abstract, you'd find that they found that stuff behind the screen with the screen at distance was more likely to cause discomfort, and stuff coming out of the screen with the screen at a short distance also more likely.
So basically you're saying that they've discovered the discomfort when viewing 3D movies has to do with the 3D effect? Amazing!
And the need to wear glasses exacerbates it, given the changes it makes to the focal point of the eyes, a core component of stereoscopic vision? Mind Blowing!
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"So basically you're saying that they've discovered the discomfort that a minority of people experience when viewing 3D movies has to do with how the 3D effect is used?"
"And the need to wear glasses to correct your vision (not the 3d glasses) is a good indicator of whether an individual will suffer from discomfort or not "
FTFY
"Mind Blowing!"
Indeed. And different from what you think it is.
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No, they needed an experiment to show that the effect was reproducible in a controlled environment and to gain some idea of what causes it. For example, they can now say it is not a matter of incorrect focus between two cameras, psychosomatic, or just the result of really bad movies trying to use the wow factor to scrape together a decent return in the box office.
More importantly, the problem appears to be intrinsic to the current 3-D projection systems. It's not going to be fixed through incremental improv
Re:24 people? (Score:5, Insightful)
What's worse: The article says less than the obvious can go. It doesn't say anything about the effect of jumps between scenes of different depth, about stereo strobbing effects that appear when using a small frame rate, the straining effects of overly dark 3D displays in some cinemas, etc.
And with so little people you can't correlate personal characteristics of the viewers with the strain and headaches - I'm a sensitive person, and I get headaches from watching a normal cinema from too close or from an unusual angle, from watching a LCD monitor when the other lights are out, from using a closeup display (e.g. cellphone) in a moving vehicle, and I don't have any issue with 3D unless some exacerbating effects are present as well, which in my case would be dark picture or the screen being too close.
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The sample size is sufficient (Score:5, Informative)
Yes, the sample size is "statistically valid." You can show a statistically significant result using any sample size; using a smaller sample simply means you need stronger evidence to show the same significance. There are some specious statistics in the paper, but this criticism is plainly false.
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I don't think that's necessary, but the people who think his post is insightful should read this blog post: http://zedshaw.com/essays/programmer_stats.html [zedshaw.com]
Re:24 people? (Score:5, Informative)
in ui design I learned that people are sufficiently similar that you can test on 7 randomly chosen subject and if your ui work on all of them it will be good for 95% of the population, those 5% be damned. People are not that different inside so unless you are looking for a 1/100000 effect you don't need a big sample, around 30 will be sufficient in most of the case, I don't remember the mathematical proof but it exist.
However if your are doing a research on something with a great variance like food preferences you will need a bigger sample. You can read more about the optimal sample size in those paper : http://www.ime.usp.br/~abe/ICOTS7/Proceedings/PDFs/InvitedPapers/3J3_ALIA.pdf [ime.usp.br] and http://nordbotten.com/articles/OptSampleSize.pdf [nordbotten.com]
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in ui design I learned that people are sufficiently similar that you can test on 7 randomly chosen subject and if your ui work on all of them it will be good for 95% of the population, those 5% be damned....
Well that explains why UI's seem to suck.
7 random people isn't going to represent 95% of the population.
Re:24 people? (Score:5, Insightful)
Why do research like this on just 24 people?
Because you have to start somewhere. If all human studies used hundreds or thousands of people you'd have not even 1/100th as much research done. We don't have an infinite amount of cash or of decent scientists.
That is NOT a statistically valid sample size.
I somehow think the good people of UC-Berkeley realize that 24 people is a small sample. Studies of this size are usually done to suggest and design further studies, or because the premise is interesting but that particular team doesn't have the resources for a larger study; everyone who matters understands that these small trials rarely prove anything at all. It's just arrogant and ignorant to trot out sample size arguments in response to every single damn study with less than 1,000 people as if it proves you're smarter than every scientist and grant reviewer involved.
Furthermore, sample size isn't everything. If I pulled 24 frogs all with 13 legs a piece from a lake that I knew to contain 150,000 frogs I would not think "that is NOT a statistically valid sample size", I would think "Jesus Sideways-Hopping Christ, somethings wrong with this lake!". It's quite possible to get data from a small sample that is quite clear and quite certain. Many amazing discoveries in physiology have been made with sample sizes in the single digits. They had to be reproduced with hundreds of other samples by dozens of other people to check method and provide absolute certainty, but they were effectively undeniable as originally published.
The annoying thing is people dumb enough to read a study done on 24 people with any ambiguity at all in the results and go on reporting that it's a new discovery. Well, that and insouciant bastards like you who get off on thinking they're smarter than entire research departments.
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You probably meant statistical significance and it doesn't just depend on the sample size. It also depends on the noise and error in the thing being studied.
You don't know how grant money works. It's not really possible to spend grant money on ho
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Actually no, if you remembered anything from statistics class then you would know that if all the results from the 24 people had a strong correlation then the research team could easily end up having a certainty value in the very high 90s
In fact as long as you are not seeing any real outlines in then data then everyone after like the 21st person really only contributes to a tiny-tiny bump in certainty.
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It's called a preliminary study. It's not a bad idea to work out kinks in methodology and to make sure you're measuring something useful before committing resources to a study on thousands of people, don't you think?
Statistical validity (Score:2)
You should take a course in statistics. One thing you will learn is that there is no fixed number that constitutes a "statistically valid" sample size; it depends upon the standard deviation of the population, which can differ for different types of measurements. Moreover, a sample size may be too small to be valid for one study design, but perfectly fine for another study design. For example, very often individuals
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