Monday, March 5, 2012

Underbust Survey - Part 2: Sample Bias & Methodology

Part 1, Part 2, Part 3, Part 4, Part 5

I had so many wonderful comments at questions in my last post that I wanted to address them fully here in a new post.  After work tonight I'll be able to respond to each person individually.  Additionally,  I still have quite a bit of data to weed through so there will be more posts to come.

Sample Bias

What some of you don't know is that no only did I post this survey on my blog but I also posted it in a Weight Loss Forum that I belong to where the women would not necessarily have large breasts or small band sizes.  Unfortunately, I don't have the data on the percentage of women who filled out this survey because of my blog vs. the percentage who filled it out because of the weight loss forum.  However, I do have data on the Bust size of the women surveyed and I will post that in an upcoming post. 

Additionally, I found that within the healthy range it appears that my statistics reconfirm previous data.  The Marines have published data: from 1995 where they did a study that included taking the underbust measurements of women.

To be in the marines you must be under certain weight (depending on your height) and that weight falls within only the healthy BMI range.  According to their data the average female ribcage measurements is 30".  That fits perfectly with my data.  The owner of bratabase has also agreed to compare the statistics on the site to my data (don't worry, individual data will not be released or posted here, just the averages from that site) and I will be posting that comparison eventually. 

If anybody has further information regarding the average underbust measurements of women in the overweight and obese weight ranges I would be very happy to cite them here and compare them to my data.  Either post the link in the comments or email me at

Assumption Underbust=Band Size

I stand by my decision to use underbust=band size.  I very much agree that on an individual level it is best to try on bras and be aware of what a proper fitting bra feels like.  I, myself, need to go down a band size from my underbust measurement so I am quite aware of this. :) 

That being said, I would assume on average the the number of women who need to go down a band size are roughly equal to the number of women who need to go up a band size.  Thus, I think this is a fair assumption.  Realize that I conducted this survey to pass on to bra manufacturers and retailers to point out what sizes are needed vs. what they are providing. Thus, I'm looking more at averages rather than on an individual basis.

Certainly, a better study could be conducted by measuring women in person (I imagine there also is some error built in because women measured themselves and some women will pull the measuring tape tighter than others).  However, I do not have the funds for that or the resources and I wanted to get the ball rolling on this.  Additionally, this brings up the question of how would you get an accurate measurement of women as a population as a whole?  If stores like Bravissimo were to do this they would probably have a much larger sample bias than my study because it would be exclusively made up with women who had at least some concept of proper bra fittings and were most likely large busted.  If more mainstreams stores did this you would then have a bias towards larger bands/smaller busts.  One advantage of my online survey is that I do get a larger chunk of the population because I have a significant number of international readers and readers who come to my blog for the weight loss discussions/fashion advice not just for having a large bust size. 

I made the assumption that my readers understand about proper bra fitting and how essential it is, especially once you go up in cup sizes.  If you question about this I suggest you check out:
- my links in Finding Bras that Fit,
-look at this video over at FullerFigureFullerBust,
-Pictures of a Well-fitting Bra vs. Poorly Fitting bra,
- and see the difference here that a well-fitting bra can make in terms of support and uplift.
Personally, I find that a band that is just one band size too big can give me severe back pain and my own mother has had a breast reduction due to back pain.  Telling women that they need to add 4/5 inches to their underbust size is outdated advice from a time when bands were not made out of strechy material like they are today and it is not practical as a starting point.  While some women may need to go up a band size or two due to having a ribcage that widens from their underbust, many of us need to go down a band size or two due to having a smaller ribcage than their underbust measurement.  When you get into the plus-sized range you have further issues because it depends on how squishable your back is (for instance, a women who naturally has a wider ribcage vs. one who has a larger amount of fat covering her ribcage might have very different needs for their band size). 

Using BMI

Astrid pointed out that it might be interesting to redo the results with waist measurements and I agree and had already planned this.  Typically 35" and above is considered the "unhealthy region" for a waist measurement and below 35" is considered healthy so in this case I split the the band sizes in two groups.  Unfortunately, a number of respondents didn't know their waist size (34 to be exact) but we still had a good deal who did.

When talking about percentages, 87.03% of respondents had waists < 35" whereas 12.97% of respondents had waists >= 35".   Looking at the data by waist size we see much more of a distinction between the two groups:

In the top figure one can clearly see that, again, most women fit into the 24-36 band size range, 98.8% to be exact, and 88% fit into the 26-34 band size range. The most needed are 28 and 30 bands, which again match the marines' data cited above.

When we go to the >=35" category we can see fairly quickly that 36 band is the clear winner.  87.5% of women fit into the 30-44 band size range.  One thing we do see, though, is that when you increase the waist size you also deal with a wider range of band sizes.  This does place a lot of onus on plus-sized stores because they need to cover a larger range of bands in order to fit their target consumer.  However, like I mentioned in my previous post that simply is not happening.  In terms of statistics for the plus-sized women in my survey:

- 20.8% need a 32 band or under
- 33.3% need a 34 band or under
- 60.4% need a 36 band or under

Looking at these statistics, I would guess that most plus-sized stores are catering to the 35" waist women and above.  This rings true from my own experience experience when I used to shop at Lane Bryant.  However, in doing so they are missing out on a number of women who are overweight or obese.  In my survey 176 respondents provided enough data so I could calculate both their BMI and waist measurement.  Of those:

- 58.5% were in the healthy BMI range.  Of those respondents 2.9% had waist measurements over 35"
- 21.6% were in the overweight BMI range.  Of those respondents 0% had waist measurements over 35"
- 19.9% were in the obese BMI range.  Of those respondents 42.9% had waist measurements over 35"

From that we can conclude that plus-sized manufacturers are catering to a smaller chunk of the population than just women fitting into the overweight and obese range.  Rather, it's more on the order of 43% of obese women (with small percentages in other BMI categories).  Lane Bryant, for instance, has its smallest size 14 listed as corresponding to a 34" waist (although, I have to say a 35" or even 36" waist might be more accurate in my experience).  So, really, they are only catering to less than half of obese women both in terms of clothes and bras.   I should mention, though, that there might be some bias in my survey towards an hourglass frame due to the nature of this blog so that may skew respondents towards having smaller waist sizes.  If anyone knows of studies comparing waist sizes and weights I'd be interested in comparing them to my results.

I also want to mention something, though.  I wonder if the bias in terms of where a women measures her waist and how tight it is, isn't more significant than weighing oneself (especially since many women have digital scales) and a woman's height does not vary as much as a waist size (personally my waist can go up 1-2" depending on where I am in my cycle, what time of day I measure, and what I have eaten recently).  Weight also varies depending on these factors but not as significantly if one measures first thing in the morning in the nude.  Again, I think going by waist size would be more effective if we were able to measure women in person.

On a personal note

This survey is NOT meant to be a judgment on women's bodies and I am in no way whatsoever trying to criticize a certain body type.  Rather, I have long suspected that bras and clothing manufacturers are not catering to their customer base and I simply want to point this out and provide data for them to see that there are large chunks of the population that cannot find proper bras and clothes. 

If you read my blog at all you know that I have been a woman who had a waistline well over 35" ( I believe it was 38" the first time I measured it but that was already when I had started losing weight) and at my highest I used to wear very, very tight 16s from Lane Bryant.  The largest bra size that I recall wearing was a 40K.  I'm extremely thankful to bra and clothing manufacturers that cover the higher end of the band/clothing sizes and that certainly is needed also.  But I want to point out that the lower end also needs to be covered and that there is a good deal of women in that range too. :)


  1. I really love how you've addressed so many concerns and tried to present the data as straight-forwardly as possible! As I mentioned on Facebook, our sales are similar to your conclusions. Our best-selling band sizes are 32-36 which account for roughly half of our total sales. This correlates with recent findings that the average woman in the US wears a size 12/14 with a waist size of 34" (allowing for differences in band preference and body type). In contrast, 28 and 30 bands only account for 8.5% of our sales. Combined, the number of 28 and 30 bands we sell are lower than every other band size we carry in store except for 46+ band sizes. We peak at 34 (although 32 and 35 are very close behind), and then trail off in the more plus size bands. Of course, we've only been open eight months, so that information could change as we gather more customer data. Personally, I would really love to see 26 bands available, and I'd like to see more options for women with higher cup sizes too. Thanks again for taking the time collect all of this information and hopefully use it for change!

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  2. Thanks!

    I'm just now getting a chance to respond to everyone but I saw your facebook comment and I find that pretty fascinating. My suspicion is that it is due to my survey having a larger percentage of women at the lower end of the BMI scale than the average in the US (53% going purely by BMI vs. 36.5% for the US average). Interestingly enough, though, North Carolina is on the lower end of the obesity percentage: 27.8% vs. 35.7% the national average. Granted, I don't have the stats for females only so those may be higher. Additionally, the stats for overweight BMI on a state level I don't have so it could be NC has a higher percentage of overweight compared to obese individuals.

    I wonder too, if the number of 28 bands and 30 bands even amongst the overweight and obese population reflect that my blog also focuses on health and fitness so that my readers who are in the overweight/obese categories do take care of their health well and, hence, have slightly smaller measurements because of that?

    Another thing that I'm curious about, when you establish band size... if a female has a band size of 31" (for example) would she typically size up or down?

    It does make sense, though, that lingerie shops would have to vary their size selection according to the region they live in. Looking at national US stats: the state with the highest level of obesity is Mississippi at 34% whereas the lowest is Colorado at 21% so they most likely would have very different needs (I wish I had the same data by waist measurement and also overweight BMI!!!). I do wonder, though, about those stats because no state reports an obesity level over 34% but yet the national average is listed at 35.7% so something very strange is going on there...

  3. Finding a proper statistical sample is such a tough prospect anyway, and there's always going to be some bias. For us, I can tell you that a nearby Lane Bryant will actually send us customers because they do not carry a large range of sizes, which in and of itself speaks to your assertion that plus size lines are missing out on huge portions of the plus-size market. In fact, I would say that around 70% of our plus-size customers came to us from this referral. Our demographic also skews older right now with the median age being around 40. Lately, we've been trying to branch out to younger women since it is important to start wearing a correct bra size as early as possible. Majority of the women under 35 who have come to the store wear a 34 band size or lower, and this is where we see our 28/30 band size market.

    With regard to your question about in-between sizes, I've found that it depends on personal preference. Some women really like a tight band and would rather size down. Others are so used to wearing the bigger band sizes that they were improperly fit into that even sizing up to say the 32 (from a 31" measurement) still feels too tight for them. One woman should have been wearing 38s but was wearing 44s and 46s, and the lowest she would consider was a 42. This skews the band size data forus because whereas you have band size = underbust measurement, we had band size = underbust measurement + x" to allow for personal preference.

    As we're open longer and develop a more diverse customer base, then it will be interesting to report how these numbers change! Regardless, you've really done such an excellent job with all of this information, and I'm looking forward to part III!

  4. Agree with Sophisticated Pair. Even though I've been open for only three months, well over half my sales have been 32s and 34s. The biggest factor keeping my customers out of smaller band sizes is, to put it bluntly, back fat. It seems lots of women would rather sacrifice support in the front in order to get a smooth line in the back. Bras made in larger band sizes often incorporate design features that minimize "back fat", but the smaller band sizes often skip these features. So I'd like to see manufacturers not only offer more bras in smaller band sizes, but more bras *that women want to wear* in smaller band sizes. And p.s. I love your chart about waist size and band size. Would somebody please send it to Vicki's so they's stop putting size six girls into 38 bands ;-?

    1. Do you agree with Venusian Glow's hypothesis of boob migration that leads to back fat? If so, would some of these customers actually need smaller bands later on, as their tissue migrates back to their boobs?

    2. I wasn't able to read the article as the page wouldn't load, but I will say that a) I totally have back fat that is separate from breast tissue -- there's about an inch of bony ribcage between, and I've been wearing the correct bra size for at least a decade, and b) if we're talking about the underarm overhang, then, yeah, I can see that as potential breast tissue.

  5. Pencil Test, that's exactly what we see too. The smaller band gives more support, but the smaller wing doesn't give as smooth a side and back profile. I think this is one of the reasons we sell a lot of Natori's Cool Contour because it does have a very flexible, semi-wide wing so that women get a better silhouette.

  6. I'm just going to respond to everyone at once, but wow, very interesting! It sounds like there is a big play off here between support and appearance and that really may be an issue. Bras I Hate had a great post awhile back about poor bad construction and I think that might be the best route to pursue this: Personally, I'd love to see wider bands (that also include longline bras!!) in a wider array of sizes.

    One thing that you ladies touched on that I've seen for myself is that it's very, very difficult to get an amazing everyday bra that doesn't show up underneath simple T-shirts. As a mom (and someone who has lost a significant amount of weight) there's the added difficult of skin with less elasticity, and breasts that just don't stay put in low cut bras (like I discussed in my Soft vs. Firm Breast post). I can't imagine that I'm the only woman in this position but yet most brands that come in small band sizes cater to the younger crowd with firmer breasts (so brighter colors, lower cuts, less nudes etc). I certainly like a lot of those bras too but am struggling to find the perfect everyday bra for myself (although Curvy Kate's upcoming daily boost might well be a solution). I'd love to see a very practical bra (like the Fantasie moulded t-shirt bra) that comes in a 28 band, for instance.

    Never Took Home Ec that's also a good point and I wonder about that too. I still have some very slight back fat (even with having a ribcage that measures at 29") but it goes WAY down when I wear the correct cup size/band size. However, depending on the type of band (and how wide it is) I have more issues with it showing up underneath shirts.

    The Pencil test- I do plan on sending my results to many companies once I've posted them all. Now if they listen or not that's another question entirely. I'm so tempted to make a trip to Victoria's Secret on my next trip back to the states, just to see what insane size they put me in. :D

  7. I am a huge believer that the "back fat" created by wearing a properly tight band is often migrated breast tissue. I do believe band construction has something to do with it, but I think it also has a lot to do with not putting on the bra correctly, meaning not bending forward and scooping up all your breast tissue and arranging it into the cups. I think not taking the extra few minutes to put on the bra properly really contributes to ladies wearing too small cups and "back fat" overspill.

    I understand it's pretty common to see a further increase cup size a few months after wearing a tight enough band, which supports this theory.

    1. Thanks for your response. I'm thinking more and more about migrated breast tissue and am thinking about making a post on this soon. :)

  8. Really cool study. I hope I do not offend anyone by asking this. But why not use bodyfat levels, I know that the tests are not as convenient or cheap as bmi. I know that the work will take some time, but there are great statistical software programs one can use to help with the process!

    Seriously though, wouldn't a study be interesting to see if there is a correlation between the difference between band and bust size in relation to body fat levels? Someone can have a low bmi and high levels of body fat (though this is relative) and still have large breasts maybe because of their higher bodyfat levels or more breast tissue. Whereas, someone can have small breasts with a high bmi and low bodyfat levels because they are athletic. And, obviously there are a number of different possibilities.

    I really hope my question wasn't too offensive, but I think it would be an interesting study for someone to do.

    1. I definitely don't take offense to good questions. :) Basically, the reason I looked at weight (and waist size) was because they were the easiest measurements for women to take at home. I don't have access to anywhere where I can check my body fat % (or at least not for free) so I figured many women had the same dilemma.

      But I agree, it definitely would be interesting to check this. I know in my own case because I do heavy weight lifting I probably have a lower body fat percentage than the average woman at my height/weight so that could contribute to my small band size. On the other hand, I have heard that sometimes building muscle in your back can cause you to increase your band size. It's one thing I want to experiment with when I reach my goal weight. :) This is definitely an issue that should be explored further.

      Because the marine's survey is only for women who are at a healthy weight and certainly physically active it means they probably have a lower body fat percentage than the average woman at the same weight. Does that mean that the band size is smaller than because they are more muscular OR is it larger because they increased their back size due to weight training. It really is a good question to ask.

      I think the best way to do a systematic study on it would be to find women at roughly the same height and weight and compare their body fat percentage and underbust measurements. It would be interesting to see what comes out! ;)

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  10. I appreciate your efforts to work with the data you have, but I think some of your conclusions cannot be justified, because of relatively low response rates and the self-selection effect.

    Some independent local clothing stores have indicated to me that their peak sales are US sizes 14-16 skirts, and 16-18 dresses, and the bra size they report as most difficult to keep in stock, regularly selling out within a week of shipment, is size 40G.

    These sizes might (could well) represent women outside of "healthy" BMI, but if that is where the majority of sales are for women 25-ish and older, then one must suspect that the self-selection for your survey was not statistically meaningfully representative of the portion of Central Canada that I live in.

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