This is an earth-shaking book; it should be required reading. It is not a litany of rhetoric and editorializing; it is a bible of facts and statistics (that will be cited for decades to come), supporting an irrefutable picture of a gender crisis that has escaped me and escapes anyone who pretends otherwise. I'm a typical middle-aged, middle-income, white guy and I thought I had a working understanding of the gender gap. I did not. I had the typical MAMIWG surface level understanding of what I *saw*, and I can say the operative word in this book's title is *invisible*. We all know that concert theatres have inequitable lineup for the washrooms during intermission. Sure, women need stalls and take longer in general. But it never occurred to me that women are MUCH more likely to have responsibility of care children and/or seniors. That will tend to greatly extend their bathroom time and duties. These factors are cumulative. It would be revealing if the actual engineered square footage of bathroom facilities were determined by the data based on throughput of visitors by gender. How large would the women's bathroom have to be compared to the men's so that, on average, no woman - including her smaller bladder, her entourage of children/seniors/pregnancy/etc. - has to wait for a stall (let alone stand in a lineup going out the door) longer than a man? How small would the men's washroom have to be to generate a line that stretches across the foyer - long enough long that men choose just to “hold it” rather than miss the cue to return to seats? (Women do this. Did you know that? I did not.) Just one little example of a thing that was completely invisible to me. If I personally don't see it, let alone experience it, it isn't happening. This is a recurring theme of the book. Snow-plowing! We plow the roads first, right? Priority goes to the cars to get to work. Except women are much more likely to walk or bus to their places of employment. Additionally, women are much more likely to "trip-chain" combining multiple, interconnected errands such as childcare, elder-care, household shopping, etc. And they often do this burdened with baby-buggies, strollers and purchases. These things are cumulative. Unplowed sidewalks invariably make trips longer and more risky. The result is a far higher injury incidence for women than for men. Don't see it, isn't happening. It's not for want of looking - to those of us who don't *actually* walk a mile in those snow boots, it's invisible. But author Perez puts numbers to all these examples and many, many more. Female crash test dummies. Women are at much greater risk of getting injured in a car accident, because the standard crash test dummy is a 70kg, 5'9" male. Guess how many crash test dummies are pregnant. I'll leave it to the interested reader to find out when the first female crash test dummy was put in a car (hint: the 21st century) I gave up highlighting passages that I wanted to save to read to my wife in the morning. The whole book is noteworthy passages. (To *me*. She smiles and nods approvingly as I recount things she's lived her whole life.) The TLDR message of this book: we lack disaggregated data. Companies collect all sorts of data on the human condition, but don't collect data on gender. So, for example, a dataset of all drivers involved in accidents hovers around the Reference Male (70kg,5'8"), with deviations from that norm falling off to either side. Except about 95% of all women fall below that line (read the book to check my numbers), which means they vastly outnumber men in being underrepresented by the data. And this goes back a LONG time. 21st century policies are still based on arbitrary reference models that simply ignored women. The effect is cumulative. Women can't get jobs or proper healthcare or a hundred other things because we keep using data that's hopelessly outdated and hopelessly biased. Thing is: why *that* reference model? Women aren't a minority or a special interest group; they're not a fraction of the population - they're 50 percent of the human population. But for the flip of a coin, centuries ago, it could have been a (checks notes) 62kg, 5'4" woman. And why not? An alarming number of academics are on record as saying it is because women's physiology is too "complex" with too many "confounding factors". A little tip here: when a factor is 50% of your sample size, it's not a *confounding* factor; it's a *diagnostic* factor. Imagine: "Patients with arms make it difficult to assess the efficacy of our drug. Arms are a confounding factor, so we only collect data on armless patients. The drug we are releasing to the world (armless and arm-adorned alike) is based on our Reference armless patient. And we don't tell anyone this detail, of course." (*My* example, not Perez'. Perez is matter-of-fact in her approach, not facetious like me.) This is all stuff I simply did not know until I picked up this book (on a whim, no less. It came up in my list of non-fiction, and I saw the words “data bias” and thought it might make some nice reading for this numberphile.) Finally, if you want an extant example of the uphill battle faced by women in a male-dominated world, check out some of the one-star reviews (on GoodReads, where I posted this). The ones I read are so cliched I wonder how they can possibly be written by real people; they are cartoonish males that make me embarrassed. A lotta feelings in those reviews. Feeling attacked for being a white man. (How can you feel attacked by facts?) Feeling it's important to point out that Perez is a Feminist Activist (OK, first off - duh! Thanks for pointing that out for the rest of us. But also - you say that like it's A Bad Thing. Like, somehow standing up and fighting for your rights - your HUMAN rights - is to be denigrated. In what world would a rational good-hearted human NOT want a disadvantaged people to fight for the rights the rest have? WTH?) And here's the best one: several reviewers felt that Perez would benefit from their wisdom about what she *should* have written about. (What's all this about women? What about world poverty? You should be writing about that instead!) How is this not a cardboard cliche of a man condescending to 'splain to a woman what she should be doing in His Not So Humble Opinion? I am not making this up. Yeah. So. I drank the Gender Wokeness Kool-aid - and now I can't undrink it. You should too. Thank you Caroline Criado Perez for enriching my life.