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BMI - agree or disagree?

crazyravrcrazyravr Posts: 4,429Member Member Posts: 4,429Member Member
Do you agree or disagree with the Body Mass Index scale? I absolutely do not.
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  • FuzzipegFuzzipeg Posts: 1,601Member Member Posts: 1,601Member Member
    Do we have anything better? Has someone, anyone considered a different way to achieve an overview?
  • deannalfisherdeannalfisher Posts: 3,968Member, Premium Member Posts: 3,968Member, Premium Member
    as a statistical tool for looking at population measurments - no issues; as a tool that is focused on the inidividual - not so much
  • hesn92hesn92 Posts: 4,001Member Member Posts: 4,001Member Member
    It's fine. It's just a general guideline. Of course it's not going to be accurate for people that are more muscular than average. Like at one of our yearly health exams for our wellness program at work, my coworker turned out to be "overweight" but she was actually very thin and very healthy. She was just a lot more muscular than average.
  • DX2JX2DX2JX2 Posts: 1,679Member Member Posts: 1,679Member Member
    It's just a population average though it should be a reasonable estimate for about 67% of the people out there give or take, assuming that the standard deviation isn't too big a number.
  • allisonlane161allisonlane161 Posts: 219Member Member Posts: 219Member Member
    I agree that it's valid for the majority of people. I also think though it should be used for health insurance premiums with the caveat that if the applicant requests it, the insurer do a physical and determine muscle mass.
  • rheddmobilerheddmobile Posts: 2,734Member Member Posts: 2,734Member Member
    cdjs77 wrote: »
    I'll post what I posted somewhere else as the "it's meant for populations" statement is a misinterpretation of statistics that really irks me:

    People usually misinterpret what is meant when we say a statistical measure is meant for "populations." All statistical measures are meant to determine something about a population, but that doesn't mean they can't or aren't designed to assess risks on an individual level. When statisticians say something is meant to assess risks in a population, what they mean is they have taken a sample from a certain population of people in order to estimate a parameter which can then be applied to assess some probability for other individuals or groups in that population. For example, if we take a sample of university students and estimate their score on a calculus test based on how much they study for it, we have a parameter we can use to predict test scores for the population of university students based on the amount of time they study. This has two important points:

    1. Because the sample came only from university students, we can only accurately apply this statistic to the population of university students. We don't know how this applies to other people. Maybe university students already have some sort of knowledge which helps them on the test that the general population doesn't. So studying for one extra hour as a university student may increase your score by 10 percentage points, but only 2 percentage points for those with a lower education level.
    2. Just because we say this can only be applied to the population known as university students, doesn't mean we can't use it to assess outcome likelihoods for individuals. We can use it to estimate individual scores with varying degrees of accuracy, but only if the people come from our select population known as university students. Let's say our confidence level is 99%. We can use this to say that, with 99% confidence, Student A who studied for 2 hours will score 10 percentage points higher than Student B who studied for one hour.

    BMI works similarly. It estimates parameters for a "population" based on sample parameters, but that doesn't mean it was only meant to assess risks for a population as a whole. It is meant to serve as a easy way to estimate whether or not someone has a healthy body fat percentage based on certain criteria. It is accurate to within whatever confidence level is chosen when estimating these parameters and it applies to whatever individuals come from the population we estimated it from (in this case, adults of European descent). Obviously, there is an error rate, so some people will not fall into the correct categories, but error rates for scientific assessments such as these are usually no greater than 5% total (2.5% at each tail, meaning 2.5% will be classified as overfat when they are not, and 2.5% will be classified as underfat when they are not). The other thing to note is that this estimation was done at a different time, so it's very likely the estimate for a healthy BMI has changed over time, but given the fact that the western world has increased it's calorie consumption and become less active in the past few decades, it's unlikely that BMI overestimates the number of people with an unhealthy body fat percentage and more likely that it underestimates it.

    In Short: BMI is a fairly accurate predictor for the average person, and can be applied to assess risk at an individual level. It is also possible that BMI today underestimates body fat percentage categories.
    Saying it is a predictor meant for populations is a misinterpretation of how statistics works and can be applied. We use statistics derived for population assessments all the time to assess individual risk, that's how insurance rates are often calculated, and, since insurers do not regularly declare bankruptcy, it's a pretty good sign that these estimates are pretty accurate. If you're not someone who has been an athlete for a few years, BMI is very likely to be an accurate picture of your health risks, and possibly even an underestimation.


    Overall, it's an accurate predictor for most people. There is a degree of error as with any statistical prediction. Smokers have a higher risk of lung cancer, but of course not all smokers will get lung cancer. The error rate is also not particularly high. It is also one statistic and, as with any one statistic, it cannot be used as the end all be all for determining health. However if your BMI says you are overweight or obese, it's fairly likely that you are. Whether or not you will face the health consequences associated with this depends on a number of other factors.

    Not quite. To continue your analogy, just because someone hasn't studied doesn't mean the teacher gets to fail them without grading the test. YOU HAVE TO GRADE THE TEST to find out the student's grade, whatever the predictive value of studying may be. Businesses and insurance companies are not doing that today, and they should. To be very specific in language, BMI was designed as a quick and dirty tool for identifying at risk people, derived from population statistics. A similar situation might be observing students studying, and students who don't study enough getting a call from the teacher saying you should maybe study if you hope to pass the test - the teacher might not know that an individual student already knows the material from previous exposure and will do just fine.

    That's different from the current situation, getting a rise in insurance rates or a cut in your paycheck, based on a statistical prediction which may or may not apply to you.

    The percentage of misclassified people, according to the most recent studies, was significantly higher than any 2.5. It's true that the majority of people fall where they should, but not so true that the alternative should be dismissed out of hand.

  • LounmounLounmoun Posts: 7,807Member Member Posts: 7,807Member Member
    I think it is a reasonable guide to a healthy weight range for most people. I don't think it should be taken as law that someone has to be exactly within that range to be healthy. I think people should look at their personal feelings and experiences in addition to the bmi scale in determining if they are the right weight for them.

    BMI is pretty accurate for me.
  • cwolfman13cwolfman13 Posts: 34,148Member Member Posts: 34,148Member Member
    I think it's a useful indicator of potential risk, but not useful alone in determining an individuals actual health. I think it is also useful as a starting point for weight loss objectives. It is best utilized in conjunction with other measurables. I initially thought I'd have to drop down to 170-175 to get to where I wanted to be...so it was a useful for that...turned out to be wrong, but I only ever viewed it as guidance.

    I'm 5'10" and my maintenance weight is 180 which puts me about 6 Lbs overweight by BMI. At that weight I am at a comfortable and healthy 15% BF. I could most certainly lose 6 Lbs and be at the high end of my BMI and a lower BF%, but that would make no difference in my health, only my aesthetics.

    I think the vast majority of people, including myself, being in a healthy BMI range is perfectly achievable. That said, I do no more men than women who are just outside the BMI range but at a healthy BF%...all of them train in the gym and aren't typically super lean...just healthy lean. Then of course, you do have the very lean with higher than average muscle mass. Oddly, I know very few women who are outside of the BMI scale who are also at a healthy BF%.
    edited July 13
  • Spliner1969Spliner1969 Posts: 3,007Member Member Posts: 3,007Member Member
    I, personally, think it depends on muscle mass. For the average person with no weight training or just normal muscle mass yea it's probably about right. But for those of us who have built muscle, depending on how much muscle mass, it can start to be off by quite a bit. If you're really athletic then likely it's not right for you. I tend to stay barely in the overweight category even though my body fat isn't all that high right now. Admittedly it's not where I want it yet, but it's close. As I build muscle body fat % seems to be going down slowly but weight really isn't all that much. I still use BMI to gauge where I likely should be though.
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