9 ms·
> They recruited 63 healthy individuals, 135 patients with mild cognitive impairment such as memory loss, and 68 people with Alzheimer's – the most prevalent ty
by trimbo 6y ago
> They recruited 63 healthy individuals, 135 patients with mild cognitive impairment such as memory loss, and 68 people with Alzheimer's – the most prevalent type of dementia – in four hospitals in Barcelona and the metropolitan area
Wait so, N = 266? All from Barcelona?
C'mon.
- ip26 6y agoWith proper random sampling you only need something like N = 27 (I forget exactly) to reach p = 0.05 Assuming random sampling, it's a misconception that you need ten thousand participants to have a useful study.
- sillysaurusx 6y agoCue “p = 0.05 is a random choice” and a big thread about p-hacking. Any takers? It feels like everything to say has already been said about the bias of small sample sizes and the dangers of p-hacking. But it also seems like the discussion is inevitable here. I wonder if there’s a new insight to glean, somehow... For a background on why p-values are misleading, see https://youtu.be/42QuXLucH3Q https://youtu.be/42QuXLucH3Q which is excellent. He points out that 0.05 was selected by Ronald Fischer in 1925, and people have gone with it since.
- im3w1l 6y agoThe reason we have stuck with it ever since it s because it's a decent cutoff. I think in physics they sometimes use a much higher threshold of 5 sigma. Presumably because having much more data means they can afford to.
- outlace 6y agoA 5% false positive rate can be pretty high depending on the situation, like whether or not a drug is effective.
- bluejellybean 6y agoIsn't the crux just that, "proper random sampling" can be quite hard. Assumptions are fine in theory, in reality, they can seriously throw us for a loop.
- ip26 6y agoRight, so you really need to review the study's methodology to determine if N = 266 is actually enough or not. I am guessing my original parent did not conduct such a review.
- irjustin 6y agoI'm not sure which side to take on this issue. I think both can be right, but I lean towards agreement with the root comment. Root parent comment is right to question if the N=266 is truly random given the description we do have at hand. You are right to say N=266 could be truly random and we don't have enough information to definitively decide either way. We can't read the study so it's just what we have - saying you have a truly random sample with a group just from Barcelona is extremely hard to accept. I mean even you've got to admit that.
- diqwndwqiond 6y agoIt seems that his objection is he "homogeneity" of the population, they're all from Barcelona, if the sample had different locations I think he wouldn't object the small number( e.g N = 30 ).
- pvaldes 6y agoIs not just the sample. I'm worried also by the homogeneity of the researchers
- refurb 6y agoYour mixing up your statistics. Perfect random sampling of a normal distribution means you can sample 27 times and your statistical analysis is close to that of the entire population. It's highly dependent on the magnitude of the effect (when comparing two populations) and the distribution across a population. For something dementia, where even measuring the level of cognitive decline is highly subjective, no way N=27 would be enough.
- labawi 6y agoAs long as measurement errors are not significantly correlated with the tested "cause"/category, it should not have significant bearing on the results or their validity. In such a case, 27 individuals should be sufficient. That being said, article mentions 63+135+68 individuals in 4 hospitals in a single city.
- cik2e 6y agoAlso, you only need about 400 samples for 95% confidence on a proportion at the highest variance point of p1 = . 0.50. It used to drive me nuts when my CEO used to say “10 clicks out of 10,000 on this A/B test is in the noise”. No, that’s not in the noise, it’s almost certainly a clickthrough rate of close to 0.
- drumttocs8 6y agoCan you explain how N=27 could possibly represent and be extended to billions of humans? It is certainly not intuitive to me.
- wongarsu 6y agoAssuming you take 27 people from all over the world at random, and all 27 of them have two legs, you can be fairly certain that most humans have two legs. You might also conclude that about 50% are male and about 60% are from Asia, but as traits get less frequent your error bars get bigger and bigger. Of course actually picking 27 random people is extremely hard, so actual studies compensate by picking more people.
- ekianjo 6y agoRandom does not mean that it's enough to do a proper group comparison, because individual differences, genetics, lifestyle, etc... are additional factors to take in account for dementia related outcomes.
- ekianjo 6y ago> With proper random sampling you only need something like N = 27 (I forget exactly) to reach p = 0.05 will be difficult to demonstrate that they can control for all individual differences at n=266 to prove differences in dementia outcomes are linked to a single variable.
- andy_ppp 6y agoYes, I haven’t read the paper but how can you control for correlated stuff here, e.g. bilingual people are likely to be richer, more intelligent, exercise more, eat better more varied food and have richer social lives. Maybe.
- drdrey 6y agoAre immigrants and their children likely to be richer, eat better, etc?
- Koshkin 6y agoThose who are bilingual, yes.
- The_Precursor 6y ago> Those who are bilingual, yes. Wouldn't immigrants by nature have to be bilingual because they have to be able to communicate in the nation they immigrated to?
- tuatoru 6y agoGo out. Look around. Talk to some people about their parents.
- umanwizard 6y agoAt least in the US, there are millions of people who don't speak English well or at all. Source: https://www2.census.gov/library/publications/2014/acs/acs-26.pdf https://www2.census.gov/library/publications/2014/acs/acs-26...
- Franciscouzo 6y agoThere's a lot of immigration from Latin America though.
- pvaldes 6y agoPeople that speaks fluent clingon must appear in the Forbes list then.
- another1oror 6y agoAnother from Italy with 85 people that found the same https://www.alzheimers.org.uk/news/2018-05-15/bilingual-brains-are-more-resilient-dementia-cause-alzheimers-disease https://www.alzheimers.org.uk/news/2018-05-15/bilingual-brai... This one appears to have brain scans to suggest structural differences do exist
- airstrike 6y agoN = 266 isn't really that bad at all
- esperent 6y agoWhat about N = 266, all from one city?
- avip 6y agoWe did FDA cert. of medical device with way less. With sound methodology this number would be totally ok (depending on strength of measured signal)