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The BMI Is Not a Health Measure – It’s a Statistical Relic

I recently read Jordan Ellenberg’s How Not to Be Wrong: The Power of Mathematical Thinking. In it, he describes the pitfalls of linear regression, including the example of the paper “Will all Americans become overweight or obese?” According to this paper, by 2048 all Americans will be overweight or obese. This sounds dramatic – but it is statistically nonsensical. The underlying regression ignores the fact that as the number of overweight people increases, fewer and fewer slim people remain who could “convert.” Just a few years after the paper’s publication, it became clear that the increase in obesity does not follow a linear path but a logistic one – it flattens out, because populations are not infinite processes.

What Ellenberg does not mention: even the underlying metric, the Body Mass Index (BMI), is problematic. It appears in health records, insurance forms, and medical consultations – as if it were a precise health indicator. Yet it is not.

BMI as a proxy variable

To be fair: the BMI was never intended as a diagnostic tool. Adolphe Quetelet developed it in the 1830s as a statistical descriptor for populations – not for individual assessment. For decades, it was mainly used in epidemiology. It only entered clinical practice in the 1970s and 1980s, when simplicity became more important than precision.

Used correctly, the BMI is a proxy variable: not exact, but stable enough to identify patterns at the population level. And indeed, large datasets show that the risk of cardiovascular disease increases with rising BMI – but not linearly. One of the largest meta-analyses, Flegal et al. (2013, JAMA), evaluated 97 studies involving 2.88 million people. The result: overweight (BMI 25–29.9) was associated with lower mortality (Hazard Ratio 0.94). Only from BMI ≥30 did risk increase significantly. In other words: the oft-cited formula “the higher the BMI, the sicker you are” is simply wrong.

What BMI does not measure

Statistically speaking, the BMI is a noisy signal with high variance and poor construct validity. It measures mass, not health. It does not distinguish fat from muscle, nor visceral from subcutaneous fat, nor does it account for age or ethnicity. For example, Asian populations have a higher body fat percentage at the same BMI than European populations, while Black populations tend to have more muscle mass at the same BMI. A one-size-fits-all threshold makes no epidemiological sense.

Fitness matters more than weight

Barry et al. (2014) found that fit obese individuals live longer on average than unfit normal-weight individuals. Tarp et al. (2021) confirmed: among men with high fitness, obesity was not a significant mortality factor. This means: fitness has a protective effect – but not an unlimited one.

At the same time, other studies show that high fitness does not fully neutralize the effects of severe obesity – some studies find a 117% elevated mortality risk. Healthy habits improve outcomes, but they do not cancel the effects of extreme adiposity.

Confounders

A significant portion of the correlation between high BMI and health risks arises because people with obesity tend to eat less healthily, exercise less, and more often face socioeconomic burdens. Diet: people with obesity consume more highly processed foods, sugar, and saturated fats – a pattern that independently leads to metabolic disorders. Physical inactivity: independently associated with cardiovascular risk. Socioeconomic factors: poverty increases both obesity risk and limited access to healthcare.

This does not mean that adiposity has no independent effect – above a certain threshold, biological mechanisms such as chronic inflammation, insulin resistance, and hormonal disruption clearly play a role. The global data consistently show a connection (Heath 2022; Global BMI Mortality Collaboration 2023). Nevertheless: adiposity is not inherently dangerous because one is fat, but because it is usually the expression of an unhealthy lifestyle and disturbed metabolism. Beyond a certain point, however, it also becomes a biological cause in its own right.

A classic statistical error

The most common mistake in dealing with BMI is confusing population and individual. What holds true on average for a group does not necessarily apply to an individual – this is the ecological fallacy. The BMI works for groups, not for individuals: it provides useful trends, but no diagnoses.

The BMI is a prime example of a variable that can be statistically significant but conceptually weak. Or to put it differently: the BMI endures because it is convenient – not because it is good.

Stacked Area Chart: Visualizing Investments and Credit Defaults

This was more of a small programming exercise – partly because I wanted to see how things had actually developed as the number of projects going into collection increased. The data can be downloaded relatively easily from the website, but it needs to be transformed. The challenge is that the data is available per project, whereas for the stacked area chart we need to transform it so that it is available per month.

library(tidyverse)
library(lubridate)

today <- Sys.Date()

# Prepare time window
base <- portfolio %>%
  transmute(
    Loan Code
    , start_date = as.Date( Date Funded )
    , end_date = if_else(is.na( Repaid Date ), today, as.Date( Repaid Date ))
    , maturity_date = as.Date( Maturity Date )
    , invested =  Invested amount
    , status_raw = Status,
    days_late =  Days late
  )
# Calculate start of default
base2 <- base %>%
  mutate(
    late_since_raw = if_else(!is.na(days_late), today - days(days_late), as.Date(NA)),
    late_since = if_else(late_since_raw < maturity_date, maturity_date, late_since_raw),
    late_since = if_else(is.na(late_since) & status_raw == "Late", maturity_date, late_since),
    is_late = !is.na(late_since)
  )
# Create monthly sequence
months_seq <- seq(
  floor_date(min(base2$start_date), "month"),
  floor_date(today, "month"),
  by = "month"
)

# Expand: one row per loan per month
expanded <- base2 %>%
  rowwise() %>%
  mutate(month = list(months_seq[months_seq >= floor_date(start_date, "month") &
                                   months_seq <= floor_date(end_date, "month")])) %>%
  unnest(month) %>%
  mutate(
    status = case_when(
      is_late & month >= floor_date(late_since, "month") ~ "late",
      TRUE ~ "active"
    )
  )
# Aggregate per month and status
monthly <- expanded %>%
  group_by(month, status) %>%
  summarise(volume = sum(invested), .groups = "drop")

# Plot
ggplot(monthly, aes(x = month, y = volume, fill = status)) +
  geom_area(position = "stack") +
  scale_fill_manual(values = c("active" = "#4CAF50", "late" = "#F44336")) +
  scale_y_continuous(labels = scales::dollar_format(prefix = "€", big.mark = ".")) +
  labs(
    title = "Development of estateguru Portfolio",
    x = NULL, y = "Invested Volume (€)", fill = "Status"
  ) +
  theme_minimal()

As the plot clearly shows, the projects started going off the rails at the end of 2022/beginning of 2023; the €2,500 project mentioned in the previous article was overdue in January 2023. Since then, the total amount in collection has continued to grow. At the same time, you can see that I kept withdrawing money from estateguru whenever possible (each withdrawal incurs a fee, so I wait until a certain amount has accumulated).

Website Analyzer

Claude Code allows me to build applications very quickly – including ones I had always wanted to create but had kept on my to-do list for years given the time they would require. In this case, things went a step further: I first asked Google Gemini to create a SWOT analysis of Screaming Frog, and then to write a prompt that would allow me to build a better app using Claude Code. Not all features are implemented yet. But the result is a native macOS app for crawling, analyzing, and monitoring websites: the Website Analyzer. Download available on request 🙂

Here is what the app does:

Crawling

  • Recursive crawling of a website starting from a start URL
  • Configurable parallelism (1–20 workers), depth (1–50), rate limit and timeout
  • Selectable user agent (Safari, Chrome, Googlebot, custom)
  • robots.txt compliance (optional)
  • Automatic HTTPS upgrading
  • HEAD requests for resources (images, CSS, JS, fonts, media) instead of full download
  • Detection of lazy-loading images (data-src, data-lazy-src, picture, srcset)

Link Checking

  • All internal and external links are checked (HTTP status code)
  • Status classification: OK, Redirect, Dead, Timeout, Error
  • Real redirects vs. trivial ones (http to https, www, trailing slash) are distinguished
  • Embedded resources (images, CSS, JS, fonts, iFrames) from CDNs are treated as internal
  • Grouped display: same target URL from multiple source pages

Results

  • Tabular overview of all crawled pages
  • Columns: URL, Content-Type, HTTP status, size, response time, depth, indexable
  • Search, sorting, filter by Content-Type
  • Color-coded status codes and response times

Insights & Analytics

  • Site Health Score (0–100) as a visual gauge
  • HTTP status code distribution (bar chart)
  • Link status distribution (OK / Dead / Redirect / Timeout / Error)
  • Page structure by depth
  • Content-Type distribution
  • Page Speed: average, median, P90, fastest/slowest pages (top 8)
  • Dead link hotspots: pages with the most dead links
  • Link graph: interactive force-directed visualization of page connections (pan, zoom, hover tooltips)

Export

  • CSV export for pages and links (with file dialog)

Technology

  • SwiftUI + macOS native
  • GRDB.swift (SQLite) for persistent storage
  • Fuzi (libxml2) for HTML parsing
  • Swift Concurrency (async/await, Actors) for thread-safe crawling
  • SwiftUI Canvas (Metal-backed) for link graph rendering

1 Year of Working from Home

On March 13, 2020, I switched to working from home. Not voluntarily. That day, I found out that I had traveled by train the day before with a colleague who developed strong COVID-19 symptoms the next day (her test was later negative). She had come into contact with several team members. It was Friday the 13th, the day I had to send the entire team home, which caused quite a bit of fear and panic. After all, how do you get a test when the emergency hotline (116117) is constantly busy? That day, everything revolved around who the colleague had been in contact with, which routes she had taken in the office, and which rooms she had stayed in longer. A pre-defined process immediately kicked in. But for what came next, there was no process yet.

I had always been a fan of working from home and had already worked from home at least one day a week, if not two, before. Commuting was the least of my problems—I can walk to the office. But at home, I have a gigabit connection, more quiet, better concentration, and the flexibility to spend my breaks by the Elbe. Many of my interactions are video conferences with colleagues in other countries. For the first week, therefore, it wasn’t an issue at all to spend the whole time working from home. It felt like being able to eat your favorite dish for an entire week.

One week turned into a second, which was also fine. Maybe, I thought to myself, it could stay like this for a while just to be safe. Even though it became annoying that shelves were emptied and the food options became more limited. Then came the third week. Not only my team was working from home; other teams followed. And with them came the need to digitalize some processes or even build something completely new. The home office gave me enough peace to program a lot. I probably wrote some of my best lines of code during this time. At the same time, we built a kind of virtual office for our team, with a coffee corner for chatting, etc. Some highlights, like sharing our favorite music on Fridays, we didn’t have before in the office. In the summer, I met colleagues in parks (keeping a safe distance, of course), just so we could see each other in person. Meanwhile, my home office became more professional—first a monitor, then a height-adjustable desk, and several attempts to stabilize the Wi-Fi at the other end of the apartment. Fortunately, I had already pushed for converting a room into a more dedicated office space before the pandemic. Not everyone has that luxury, and I’m definitely privileged, especially when friends around me were losing income and had very different worries.

But, as with favorite dishes, if you eat them every day, you eventually get tired of them. Don’t get me wrong—I’m still a big fan of working from home. But every time I did go to the office and could meet colleagues, I came back home in a good mood. And I’m not necessarily someone who needs people around all the time. Quite the opposite. But it’s the balance that matters. The days spent working from home start to feel monotonous over time. Even though I go outside during the day, usually once at lunch and then after work, just to give the day some structure. Some colleagues struggle with separating work from personal life. And while many people think it’s cute when children burst into a video conference, it’s often embarrassing for the parent, and how are kids supposed to understand that “Dad is home but not available”?

And then there’s something else that Ronnie Grob describes well. Companies have realized that their employees can be productive even when not physically present in the office. Office space and business trips could be permanently reduced. But if remote work works so well, why not go even more remote in the future? Do we really need expensive experts on-site, or can a much more affordable expert from another continent do just as well? This is already the business model for some consulting firms—expensive consultants on-site, cheap experts elsewhere—and not only large companies have experience with offshoring or nearshoring. It’s likely this trend will continue to grow.

When the pandemic is over (hopefully soon), we will try to return to the world we had before. But that won’t be possible, at least not beneath the surface. Restaurants, unless they’ve already closed down, will reopen, and concerts will take place, but that’s just one side of the coin. Because thought processes have been set in motion that can’t be easily reversed. We’ve also learned how vulnerable our system is. This won’t be easily compensated by simply dining out more after the pandemic.

Meanwhile, I hope that the monotony of my home office will soon end and that I can once again spend well-planned workdays in the office. My fundamental hope, however, is that we will use the newfound freedom in a more meaningful way than before.

Essentialism by Greg McKeown

On one of the first pages of the book Essentialism, McKeown quotes Dieter Rams, “Less but better.” It’s hard to find a better definition of Essentialism. I am reading this book in an armchair next to the 606 shelving system designed by Rams in 1960, and when I look up from the book, I see a poster of the film Rams, which I had co-financed a few years ago through Kickstarter. I can report firsthand that it’s not enough to surround yourself with objects by Dieter Rams if you want to dedicate yourself to Essentialism. 🙂

The Essentialism defined by McKeown is based on the following core principles:

  • If you don’t set priorities in your life, someone else will do it for you. Therefore, we must learn to say “No” so we can truly make a contribution. While we don’t always have control over our options, we do have control over choosing between them. It’s about not just recognizing that you have a choice, but also celebrating the possibility of choosing. If it’s not a clear “Yes,” then it’s a clear “No.” Instead of asking how to do everything at once, the question should be asked: which problem do you want to have? Some people require more “maintenance” than others, but they steal your time and turn their problems into yours.
  • The question an Essentialist should constantly ask themselves is: “Am I investing myself in the right activities?” It’s not about getting things done (as in GTD), but about getting the right things done. A lot is less important than it initially appears. The most important and difficult things should be done first.
  • We are not designed to have so many choices and make so many decisions for ourselves. This ties into Barry Schwartz’s observations in his book The Paradox of Choice.
  • We should reflect on what we truly want, best by asking three questions:
    • What deeply inspires me?
    • What am I particularly talented at?
    • What fulfills an important need in the world?
  • McKeown suggests an iterative process: Explore, Eliminate, Execute. For Execution, it’s important to withdraw to focus. “The main thing is to keep the main thing the main thing.” The Latin origin of the word “decision” comes from “cis” or “cid,” meaning to cut or even kill. Stephen King said, writing is human, cutting is divine.
  • The most important asset we possess is ourselves—our mind, our body. We must invest in them to get the best out of ourselves. What is the obstacle preventing us from achieving what we really want?
  • The Greeks had two words for time: Chronos, the time we measure, and Kairos, the time we feel when we live in the present. The Essentialist lives time in Kairos. Multitasking is not the problem; the belief that we can multitask is. The most important question: “What is truly important in this moment?” Occasionally, when overwhelmed with many competing tasks, you must pause and see what is really important.

Overall, the points are not new; they are more of a re-compilation of what already exists. What’s nice is that McKeown brings in various historical examples to illustrate his points. At times, the book repeats itself. Still, a recommended read.

The PowerMBA: Experiences from the First International Cohort

The MBA world has intrigued me for a long time. Early in my career, I bought a book with MBA knowledge because I always felt that something was missing for me as someone with a more technical background. Not that I haven’t learned anything over the years, but I always wondered what I might be missing, something I might not even be aware of—”Unknown Knowns.” The book I bought back then was The 10-Day MBA, which I still recommend to everyone because not everything covered in it is taught in the PowerMBA. The Real-Life MBA, which is even available in German, is also worth recommending. And while we’re talking about books, The Visual MBA should not be missed.

In recent years, I’ve been bombarded with more and more ads for MBAs and alternative programs, especially for the altMBA and the PowerMBA. The altMBA seemed too expensive for what it offers, while the PowerMBA, with its introductory price of $750, was a fraction of the cost of other programs. But can something like this really be good? An unaccredited MBA? I had my doubts, as some of the topics covered were not new to me—in fact, they were quite familiar. And for any content related to “Growth Hacking” or similar topics, where long-known approaches are just rebranded under a cool new name, I find my time and money too valuable for that.

So, what about the PowerMBA? First of all: I’m not finished yet; this is an interim report. I’m writing this report because I searched for experiences from others when making my decision, but the few reviews I found online were in Spanish. So, signing up for the PowerMBA was a bit of a gamble 🙂 Perhaps my experiences will help others in making their decision.

Right after registration, you receive a certificate, even though you haven’t done anything yet. There is no application process or regulation about who can join the program. My program didn’t start immediately; a few months passed between my decision and the start. This might be different today, as I’m part of the 1st international cohort. After signing up, you’re bombarded with communities, webinars, etc., all across different apps, websites, and channels. The abundance of content is, of course, great, but having a community on one website, an app, a reading club on yet another portal—well, you get the idea. Additionally, there are Telegram chats and Zoom meetings for local groups, led by “Ambassadors,” which, of course, is a result of Corona, as in-person meetings aren’t possible right now. This means that part of the benefit of an MBA program, the offline networking, is lost.

The PowerMBA is divided into 8 modules, with the 1st module not included in the screenshot here:

The “Go to next class” button usually doesn’t work for me, even if I still have one module left. The application runs on TypeForm, so it’s not a proprietary development.

Every weekday, you get access to a video or a clickable sequence of mini-content lasting about 15 minutes, which constitutes one learning unit. This is the concept of microlearning. The unit is usually unlocked around 7 a.m., which is rather suboptimal for 5AM Club followers like me. I’ve solved this by trying to save 1-2 videos to have a bit of a buffer. In the picture below, you can see the units I’ve completed, units that have been unlocked but not completed, and units that have not yet been unlocked:

Sometimes, instead of the video, there are error messages, so it’s good to have more than one unit “on hold” if, like me, you want to do it in the morning. Honestly, I also find it a bit disappointing that more content isn’t unlocked yet, like an entire topic, because sometimes the topics are really interesting, and you just want to learn more, especially when you’re in the flow. However, this has been blocked, as the support replied to my question about unlocking more:

This I am afraid we cannot do, sorry! Our one class per day system allows all our students to progress at the same time, helping them get fully involved with the program and the other services available to them, such as the forum where they can discuss ideas or questions they may have regarding that class, with their other classmates.

This is, of course, nonsense, because I can already tell that some students are falling behind. And just because I am further along in the material doesn’t mean I can’t exchange ideas with others about previous topics. In my opinion, the quality of the exchange also depends heavily on the Ambassador and what they know about the topics to be discussed. What’s missing are case studies that you have to work on either alone or with a team.

The individual units vary in quality; some are really excellent, many are good, and a few are not so great. You can give feedback for each unit. Overall, I’m very satisfied with what I’m learning; much of it is inspiring, and I’ve already been able to successfully apply some of it at work. So, the PowerMBA has been worthwhile for me. I was already familiar with content like Lean Startup, but it’s of course cool to experience Eric Ries in the videos. Many of the first videos are hosted by PowerMBA co-founder Borja Adanero, and I can almost no longer hear “You must understand…” :), but you do have to admire the passion he brings to the topics, which is something I sometimes wish I had seen more of from professors during my studies.

In addition to the units, you get some written material, which is okay—a rough summary of the topics. Sometimes I wish for a deeper dive, but that’s not really part of the price.

The questions in the tests are sometimes just bad or at least not clear enough. This could be due to translation from Spanish, but questions like “Who wrote The Lean Startup?” are just silly. Some tests seem to have been hastily put together. So far, I’ve passed all the tests without much effort, though you do have to stay focused during the individual units, or it won’t work.

Overall, despite all the criticism, I don’t regret my decision. I’ve been able to take away some important insights. The PowerMBA is also suitable for entrepreneurs and intrapreneurs who want to start a startup inside or outside a company. Will the PowerMBA make me more attractive to employers? I don’t know. I did it because I wanted to learn more. And maybe I’ll even do a proper MBA afterward. But so far, I would definitely recommend the PowerMBA as a basic education. I will update this text when I’m finished with the program.