If all laymen knew that n is irrelevant, it's the effect size that matters, we would be in a world of good.
If the difference between means is large compared to the standard deviation of the population under study, you need less n.
Another fun fact: All groups are different given large enough n.
Edit: I'm not endorsing the study - just pointing out that n should not be the most critical thing you look for when evaluating a study. The study is fine as a simple quasi-experiment, testing the hypothesis by induction. I don't see anyone claiming causal links here. Now a study testing the hypothesis deductively needs to be designed.
While I'm sure more sleep probably does boost fitness (and cognitive) performance, this study is pretty narrow in scope and tracks results of a women's tennis team. About the only semi-useful metric they track is the sprint times, but even that isn't very useful because the researchers didn't have a third phase of the study where the women were asked to decrease their sleep back to stage 1 amounts. Having a third stage would help control for performance increase due to practice time. The other metrics they track are highly variable in a sport such as tennis because players can put speeds and spins on the ball to affect the outcome. To control for this, you'd probably have to track a player's performance in a series of matches against the same opponent in addition to having a stage 3 like I described above. Still, tennis is more skill-based and less fitness-based compared to other sports like running, so I think it would be hard to draw conclusions from a study like this.
I've got to disagree there. Sprinting around chasing a tiny yellow ball and hitting it is extremely fitness based. This is especially true of a top ranked tennis team like the Stanford women. The players on that team are already going to be pretty good, and most likely are not going to have an overall increase of that large a % over the course of a few months of training. (These women have most likely been playing tennis for years and they keep up with their training in the off season, it isn't like highschool where the team has a month of everyone 'getting back into shape').
A criticism that you could have is that 'fitness' is very ill defined. Are we measuring sheer physical endurance or ability at a physical task? I mean, your brain is connected to the rest of your body, and it governs your body's functioning. For purposes, it is just another body part (albeit an important one). So it strikes me as strange that we would really even want to measure mental ability separately from physical ability, as they are pretty much impossible to measure independently.
I have a lot of experience with this. Did three Ironman tri's (with 12 half-IM's thrown in for training) during my late 20's.
While training for the first Ironman, I changed jobs to one that required a commute and a fixed "out the door" time to beat traffic. After starting this, every Friday was cold-day. I'd get so rundown from a lack of sleep, only 8 hours/night, that I'd get a cold every Friday. After knocking off for 10+ on Friday night it'd be gone Saturday.
Sleep is also prominent in modern training programs. The old school train-till-you-die method of unfocused bulk mileage and little rest is gone. Nowadays endurance athletes have narrowly focused training workouts (speed work, intervals, weights, long & easy, etc) with a balance of days off and entire weeks of reduced training volume for recovery where the emphasis is put on rest so the body can rebuild and prepare for the next training cycle.
I don't see how athletes in what rjett calls fitness-based sports can scan sleep without impairing their health. I recall studies from years ago that showed athletes requiring more sleep than the general population.
I wish I could just "extend my sleep to 10 hours a night". However tired I am, I don't seem to be able to sleep more than 7, sometimes 8 hours tops - I just wake up naturally even if there are no sounds, distractions etc.
I don't have problems with having a 1.5-2 hrs nap during the day, but even if I have no naps and am very tired by evening, and go to sleep when I feel like going to sleep - I'll be awake in 7-8 hours and won't be able to sleep more.
My wife, on the other hand, is quite happy to sleep up to 11 hours whenever she gets a chance ...
Their rate of improvement over a 5-6 week period increased, but the article omits their baseline rate of improvement (presumably they're still-developing athletes). I didn't check if the actual study addresses this, and in any case, the improvements sound larger than usual.
Of course, it's also nearly impossible to create a placebo 10-hours-sleep intervention :)
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[ 1.9 ms ] story [ 41.5 ms ] threadIf the difference between means is large compared to the standard deviation of the population under study, you need less n.
Another fun fact: All groups are different given large enough n.
Edit: I'm not endorsing the study - just pointing out that n should not be the most critical thing you look for when evaluating a study. The study is fine as a simple quasi-experiment, testing the hypothesis by induction. I don't see anyone claiming causal links here. Now a study testing the hypothesis deductively needs to be designed.
I don't suspect any school below a rank of 15 would be taken seriously.
A criticism that you could have is that 'fitness' is very ill defined. Are we measuring sheer physical endurance or ability at a physical task? I mean, your brain is connected to the rest of your body, and it governs your body's functioning. For purposes, it is just another body part (albeit an important one). So it strikes me as strange that we would really even want to measure mental ability separately from physical ability, as they are pretty much impossible to measure independently.
While training for the first Ironman, I changed jobs to one that required a commute and a fixed "out the door" time to beat traffic. After starting this, every Friday was cold-day. I'd get so rundown from a lack of sleep, only 8 hours/night, that I'd get a cold every Friday. After knocking off for 10+ on Friday night it'd be gone Saturday.
Sleep is also prominent in modern training programs. The old school train-till-you-die method of unfocused bulk mileage and little rest is gone. Nowadays endurance athletes have narrowly focused training workouts (speed work, intervals, weights, long & easy, etc) with a balance of days off and entire weeks of reduced training volume for recovery where the emphasis is put on rest so the body can rebuild and prepare for the next training cycle.
He's long-winded but his views are definitely founded on scientific research.
My wife, on the other hand, is quite happy to sleep up to 11 hours whenever she gets a chance ...
Of course, it's also nearly impossible to create a placebo 10-hours-sleep intervention :)