I had an idea involving a society where LGBTQ individuals are more accepted than in our own world, but I need advice on the population ratios. I heard somewhere that somewhere around 90% of people qualify as heterosexual, how accurate is this, and roughly how would the LGBTQ individuals be divided up (how many would identify as gay, bi, genderfluid, genderqueer, transgender, non-binary, more than one of the above, etc.)?
You have two things you want to know about, sexuality and gender identity.
For sexuality, I think there is no easy way of getting a statistic since I believe this is a spectrum rather than an x/y/z option thing. Additionally, a lot of people are not open about where they stand on this spectrum, so your statistics would not be representable at all either. (Think gay people in religious communities and such, there is still lots of prejudice and stereotypes around it as well, and not everybody wants to lead the life of an outcast and choose to hide it rather than show it).
For the gender identity, if your society has different norms about it then ours from the start, it would be vastly different and not a big deal at all like it is today. It would be as common to them as m/f is to us. So everybody would use the other variant of gender identification, whether they identify as m/f or something else. You can not use data from our world/ cultures for that, because we are heavily biased. We are brought up with the strong idea that we have two genders and only a small part of the population defies that idea.
If we were brought up with a bigger set of 'standard' genders, much more people would be deviating from the m/f norm, because in that culture it would be the norm.
In your world, there would not be a perception of LGQBT or whatever, because everything would be normal. At that point, it becomes more of a philosophical debate and lots of guesswork about how people in such a world would act.
I believe people would focus more on liking and disliking others based on character rather than gender and sexuality. But it could also be that being straight is the minority and seen as a sin. We don't know and every theory is as good as the next one at this point.
Your problem, of course, is that there is no scientific method for definitively determining who is, and who is not, of any gender-preference/identity
And without it we're guessing something awful. It's easy to determine who is biologically male or female, you look at the plumbing.1
But without a definitive scientific test what we have to work with is only what people claim to be — and people are absolutely notorious for claiming to be anything and everything as it suits them. Who's to say if anyone claiming to be LGBT really is, or have allowed themselves to be behaviorally swayed that way, or simply chosen to be that way to bask in political popularity?
So, what statistics do we have to work with?
Popular media has claimed a large number of statistics over the years. Back when the same-sex marriage debate was underway in the U.S. the favored number was 2% of the population. Today, Wiki reports 3.8% with a high estimate of 8.6% in Washington D.C. The reason these numbers are so all-over-the-map is that the only way we have to know is to ask someone "are you LGBT?" and then trust their answer to be accurate.2
Factually, 1.7% of children are born intersex, meaning the plumbing isn't deterministic and it's a bit of a guess as to what gender they really are (remember, there's no determinstic test).
Evolutionarily, let's look at it from what I'll call scientific guesswork. Scientific, because I'll use some actual facts. Guesswork because there's no actual corrolation and therefore it's nothing more than guesswork.
From an evolutionary perspective, the tendency to not propagate the species would have been bred out of the human genome shortly after the tendency to not eat. In our earliest evolutionary forms we would not have had the reasoning power to behaviorally avoid or modify our nature. Said more simply, an animal drawn to the same gender would simply follow around and have intercourse with the same gender. End result: no progeny.
That means the likelihood of that particular genetic condition activating in any particular birth would be rare. Really rare.
How rare? The most common form of Achondroplasia (dwarfism) occurs in an average 1:27,500 births. Remember, this is the most common form of dwarfism. True homosexuality (inclusive of all LGBTism) would be more rare than this, but let's roll with it for a moment.
1:27,500 is the same as 0.0036% of the world population3 — and they want and do propagate the species.
Therefore, let's assume that factual LGBTism is no more common than a known and genetically detectable condition such as Achondroplasia.
Which brings us to the question, what is the nature of your fictional world?
Factually, using scientific guesswork, factual non-heterosexuality is 0.0036% of the population.
Factually, 1.7% of children are born intersex, the number representing a best-case reflection of what could be called a genetically similar circumstance. This is probably the single best statistic to suggest the factual percentage of LGBTism is larger than 0.0036%.
Perceptually, accounting only for what people claim based on their own perceptions of themselves, non-heterosexuality is about 4% of the population.
Which means we need to understand the nature of your world. Does it have the ability to determine the true genetics of its people? If yes, the percentage could be quite low. If no, the percentage could be quite high. Does it celebrate the freedom to choose sexual expression without social or political consequence? Then the percentage could be very high.
1 Which any doctor will tell you is occasionally not that simple as some children (about 1.7%) are born intersex, meaning the plumbing is wonky. I'll use this again in my conclusion.
2: One of my first introductions to Stack Exchange was this post on Parenting.SE about intentionally raising a child to be homosexual regardless its actual gender preference. When you have people willingly acting this way, it's no wonder that 33% "average people" think a whopping 25% of the population is homosexual.
3 Which suggests the actual number of factual LGBT people in the U.S. is about 12,000. This statement is prone to cause fights in some bars.
The ratio varies pretty wildly.
- People move around. LGBT's especially tend to cluster in a few places where they can practice their own culture. For example, the ratio will be higher in Manhattan than North Dakota.
- We don't actually know what causes homosexuality. Most people accept that people are 'born that way', but there are plenty who become homosexual while in prison, then go back when they get out.
- There is poor historical data. While we know that people were freaky since Socrates, we haven't been counting things like this for very long, and the numbers are heavily influenced by culture. There will always be some that do not report accurately. How many? Well, how many deer did you not-see on your way to work?
- As far as I know, we don't know what causes homosexuality. It could be a recessive gene, or a common mutation (like dwarfism), or it could be additives in the water. Maybe some kids just played with glitter too much. Who knows?
For the purpose of your story, make it whatever you like. Perhaps aliens abducted all the people on cape cod and used them to start a colony - now that colony is 25% gay.