My 1,000 word essay on why BMI isn't useful for a sample size of 1
Themajez
Posts: 61 Member
10
Replies
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Who decided that 25% bf was the cutoff point for excess adiposity? In men that's already pretty damn high imo.8
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So for 75% the numbers are in sync.9
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I guess it all depends on how you choose to define “useful”.10
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Useful for what?7
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There were two people in the sample with 0% body fat. Is that really possible? I mean, I assume you had to be alive to get into the sample.18
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lynn_glenmont wrote: »There were two people in the sample with 0% body fat. Is that really possible? I mean, I assume you had to be alive to get into the sample.
Looks like 8 people between 2% and 3% bodyfat too, and a total of around 24-25 people at 5% or less bodyfat. And as @lorrpb observed, it looks like the vast majority of subjects were (unsurprisingly) not in the two quadrants identified as outliers.9 -
It looks like a typical elliptical galaxy to me9
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I want to know what the person with 3% body fat and BMI 26 actually looks like.18
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You would know an extreme outlier at a glance. Most people aren't. No generalized average is really "useful" for a sample size of 1 outlier, including metabolic rate, yet we find MFP useful and don't write off metabolic rate calculations are useless. If someone has a higher/lower metabolic rate than predicted, they just make adjustments to their intake. Similarly, if someone has a higher/lower body fat than predicted, they can choose to maintain at a lower/higher BMI. As a general guideline for most, BMI is useful. It's a large range, not a single number.
I think part of BMI hate is that some people don't like to be told they're overweight (they consider it a negative word that means more than it does). In many (not all) cases, those who consider themselves outliers actually aren't, they just like a weight/body look that doesn't align well with what they want to see on the BMI scale and don't want to be described as having a "character defect".25 -
I was overweight by 25 pounds in 2016. Am a size 2 and was back then as well. I had a huge blockage in my intestines that had to be removed. Lost the weight immediately. BMI is not helpful.
Edit: Woo= denial. Lol. It's ok if you don't believe me. My medical records are stashed away anyways
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I keep coming back in hope that I find 1000 words.... Where are they?15
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I'm a sample size of 1, and I find the chart pretty useful actually, so thanks anyway.4
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Beware the lessons learned from small samples...5
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KrazyKrissyy wrote: »I was overweight by 25 pounds in 2016. Am a size 2 and was back then as well. I had a huge blockage in my intestines that had to be removed. Lost the weight immediately. BMI is not helpful.
Edit: Woo= denial. Lol. It's ok if you don't believe me. My medical records are stashed away anyways
I did not woo, but I can speculate why someone would. It's not that they don't believe you, it's that this is a medical case so it's automatically not the norm, just like protein recommendations being helpful even when there are people who have medical conditions where they need to severely limit protein intake.
Out of curiosity, you're a size 2 and a 25 BMI right now? In that case, you're an extreme outlier even without the medical issues you had.8 -
livingleanlivingclean wrote: »I keep coming back in hope that I find 1000 words.... Where are they?
I'm guessing they were going for 'a picture paints a thousand words'. 'Cept this one doesn't...8 -
This graphic isn't actually all that useful except for trying to look shocking. How many sample points are there? There is so much overlap in the middle it's hard to tell if the people misidentified by BMI are 50% of the sample or 10%. Also, BMI is useful for exactly what it was intended for: making predictions about individuals and identifying individuals whose BMI warrants further investigation. Of course it misindetifies some individuals, all statistics do, even diagnostic tests do. When you have a diagnostic test that has an accuracy of 98%, that means 2% will not be diagnosed when they actually have the disease, it also means there is another percentage (unstated) of people who will be diagnosed who do not have the disease.
Another point is that you use 25 as the cutoff, and while 25 is generally considered overweight, the real concerns start with obesity or a BMI of 30, which, if you moved the lines, you would notice significantly reduces the error rate.
It's not the BMI is not useful, it's that people do not understand what BMI was meant to be used for. It's a predictive statistic meant to identify individuals at risk of obesity and other related conditions. Being at risk does not mean that you are definitely obese, or definitely going to suffer conditions associated with a high BMI, it does, however, mean the chances are higher. The only reason BMI is a discussion, is because human beings have difficulty understanding statistics, risk and probability, and therefore misinterpret and misapply it. (That, and probably also a bit of being in denial).21 -
All I keep hearing in these kinds of threads is the equivalent to a heavy smoker going "your recommendations are useless because I don't have lung cancer".19
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That picture looks just like you yanked it straight from an introductory statistics textbook, with the title "strong positive correlation "15
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amusedmonkey wrote: »KrazyKrissyy wrote: »I was overweight by 25 pounds in 2016. Am a size 2 and was back then as well. I had a huge blockage in my intestines that had to be removed. Lost the weight immediately. BMI is not helpful.
Edit: Woo= denial. Lol. It's ok if you don't believe me. My medical records are stashed away anyways
I did not woo, but I can speculate why someone would. It's not that they don't believe you, it's that this is a medical case so it's automatically not the norm, just like protein recommendations being helpful even when there are people who have medical conditions where they need to severely limit protein intake.
Out of curiosity, you're a size 2 and a 25 BMI right now? In that case, you're an extreme outlier even without the medical issues you had.
My BMI was 25 back in 2016 (I mentioned that already). Its not anymore. The blockage is gone.3 -
OK, so it looks like we have established that BMI is not useful because I'm assuming it's not predictably accurate for:
- Women with 25 lb intestinal blockages.
- Two individuals who according to OP's graphic seem to have 0% bodyfat, which is likely physically impossible.
- Bob and Roger.
BMI is a guideline that works quite well when considered as part of a group of measurements, like weight, BF%, waist measurement, activity level, fitness level, BP, resting heart rate, etc. Most if not all of those measurements are generally useful but can be misleading for any one individual if viewed on it's own. A minimally intelligent person with a genuine desire to quantify their individual level of health is more than capable of considering some or even all of these measurements with the help of their doctor to reach a meaningful conclusion. There is no one measurement, nor is it reasonable to expect there to be, that can fully express the entirety of an individual's health.
While the OP doesn't mention it, I agree that the insurance industry's reliance on BMI is wrong headed.
If you are grouchy because you think your weight is fine but you still fall in the overweight or obese BMI, do the work of getting those other measurements taken. I'd bet for the vast majority of the people in that situation, they'll find that several other markers will tell them they need to lose weight. If not, congratulations, you're an outlier. Maybe get that on a tee shirt or something.
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KrazyKrissyy wrote: »amusedmonkey wrote: »KrazyKrissyy wrote: »I was overweight by 25 pounds in 2016. Am a size 2 and was back then as well. I had a huge blockage in my intestines that had to be removed. Lost the weight immediately. BMI is not helpful.
Edit: Woo= denial. Lol. It's ok if you don't believe me. My medical records are stashed away anyways
I did not woo, but I can speculate why someone would. It's not that they don't believe you, it's that this is a medical case so it's automatically not the norm, just like protein recommendations being helpful even when there are people who have medical conditions where they need to severely limit protein intake.
Out of curiosity, you're a size 2 and a 25 BMI right now? In that case, you're an extreme outlier even without the medical issues you had.
My BMI was 25 back in 2016 (I mentioned that already). Its not anymore. The blockage is gone.
I must have misunderstood then. I thought you were 25 pounds overweight, which would mean way higher than 25 BMI. Even with your condition, you were only a fraction of a pound overweight. Goes to show how wide of a range normal BMI has to accommodate most people.5 -
KrazyKrissyy wrote: »I was overweight by 25 pounds in 2016. Am a size 2 and was back then as well. I had a huge blockage in my intestines that had to be removed. Lost the weight immediately. BMI is not helpful.
Edit: Woo= denial. Lol. It's ok if you don't believe me. My medical records are stashed away anyways
You would classify as an outlier with that type of medical condition.
NEXT.6 -
It is practical to reduce people to numbers when you are dealing with large populations. It is also practical to generate those numbers using simple formulas based on easily obtained and available data. That is what BMI is for...large scale population evaluations. It is useful for that. It is not practical to run around body-calipering or DEXA scanning millions of people.10
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I would initially evaluate the data and methodology used to obtain it. The data needs scrutinized before making a pretty picture. It means nothing without knowing the DOE controls.
People are impressed with charts and graphs and lots of data points and...I'm not sure why, other than they look good at a glance. They are only as good (or bad?) as the data they are derived from. I'll step off my technical soapbox now.
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The post is 2 years old. Nothing wrong with resurrecting old threads, but just letting you know.
I like BMI as a concept. A lot. The clarity and simplicity of it. If you're Class III obese, that means what it means. If you're Normal, that means what it means, too.
When I go to a doctor appt, the top page of my care summary, upper right hand corner in big, bold font: BMI and BP. Everything else like my aches and pains are footnotes to that header info for my physician. BMI is what docs use to get their snapshot of your health risks. It's what insurance companies use to gauge how long you're going to live, based on their actuarial tables.
I love how BMI syncs with clothing sizes, at least in my case. Class III obese, where I started my diet = men's 3x. Class II obese = 2x. Class I obese = XL. Presumably, when I get there, Overweight = L. I can tell from BMI what size to buy LOL
Never understood the antagonism to BMI here on MFP. Sure, there are outliers with unusual body compositions that don't fit neatly on a BMI chart - phenomenally conditioned bodybuilders who are classified as "obese" when they are just ripped, for example. But for us average Joes and Janes, BMI provides a useful, simple, clear snapshot of things. And no one ever said BMI tells you how healthy you are. The only thing that's ever been claimed is that a higher BMI has a statistically demonstrated correlation to various ailments, which we'd like to avoid.9 -
Leaving aside OP's chart - because I am not a graph person and I dont really understand what it is saying and it has obvious inaccuracies if it includes subjects with 0% body fat
I dont get the antagonism either.
BMI is a useful guide for the vast majority of people - and for those who are genuine outliers, this is obvious both to themselves and their doctors.
Does anyone really not know, or think a doctor would not see, that they are an elite body builder or an amputee or a person with dwarfism or 9 months pregnant or have a huge instestinal tumour or any other reason why standard BMI calculations would not apply to them??
So, sure, in OP's words, BMI is not a useful number for those n = 1 people.
No kidding.
My own n=1 - as a not very muscular middle aged woman with a BMI of 28 - both my doctor and myself and any casual observer could tell it wasnt an abnormal amount of muscle or a medical condition - I was plain old over weight.
am healthier now and less likely to develop weight related medical conditions, with a BMI of 23.10
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