When I got back into chickens I went to a commercial hatchery and had them sexed. Sexing was 100% as ordered. When I went heritage breed they were straight run from the breeder. The ratio on both orders was 12/13 and 13/12. I was satisfied with that.
I got 5 chicks all pullets, and 5 chicks straight run, plus ended up being given 2 mystery chicks. They ALL ended up pullets. I really wanted a male and ended up having to find a rooster on craigslist. So I think it's just a crapshoot and some people are just luckier than others. I think mine were from Cackle (ordered thru a feed store- was either cackle or ideal)
I know this is an old thread but when I was in school in a 10th grade biology class (so we are pushing 25 years here) I remember being told that if you thought a pregnant woman has a 50/50 chance at either sex you are wrong, it is actually slightly higher odds for boys, but due to genetic inherited diseases and wars the world has a slightly higher percentage of females I think it was 52 percent females and 48 males on the planet and the pregnancies where like 55 % male, and then live births it slipped to something like 52 or 53 percent male births. The teacher showed a chart (within 3-5 years before I had the class) that showed in most species it is slightly higher male births and a few where slightly more female, tho not many. I figure the hatcheries know it is more than likely 52-55 male chicks out of 100 but they may up it to 59-60 so not ti tick off too many buying straight run. also they almost all advertise 90% accuracy on sexed birds, I figure unless it's a newbie on the sexing line they can get it 98-99% (1 or 2 per 100 either a mistake by the employee, or one looking like the opposite gender) and they throw a few more males into a batch of 100 to get rid of them. I have seen many posts on these threads about people buying the "fry pan specials" or however they phrase it from the hatcheries, and they say it's almost all roos on the hatchery website but many people here have gotten all roosters or maybe 1 or 2 hens at most. if it's 90% accurate, other than if you get all sex links why wouldn't they get 10% hens (of the non-sex links)???? So if I get 80 non-sex links I would think 90% would mean 8 hens (approx.) or at least 4 or 5., not 0 (again you play the odds they may send you 100 sex links and you accept that risk buying that type of special).