Yes, absolutely. That's why you also look at things like the distribution of birth day digits, which is something you expect to be standard in almost every dat

Yes, absolutely. That's why you also look at things like the distribution of birth day digits, which is something you expect to be standard in almost every data collection that didn't directly use that as an explicit selection factor. But regardless, back to gender. Lots of groups don't have 50/50 splits. But where they don't, it's elementary to discover that they don't. Plus it's a peice of information that is traditionally very accurately recorded: recording mistakes and misreporting compared to other variables in practice is almost traditionally the lowest of any variable amongst most populations of social data. How much they differ from 50/50, and why they differ is usually a big peice of the analytical puzzle. Someone else pointed out "well, professional footballers all men". But that's exactly my point, if you were generally interested in discovering things analytically, and you got a set of data sources from professional footballers, you'd discover all men, and quite rightly you'd investigate and find out "yeah, gender plays a real role in professional football". There's actual mechanisms and predictions you'd eventually find. But in this situation, where you're explaining birth order effects, we need to start hypothesising and looking for tests, falsifiable claims, and mechanisms of operation. Now, I don't know what mechanism is at work here, but you can bet that an almost 100 make presentation rate amongst a survey that didn't explicitly select for it is highly relevant to the puzzle. Why is it attracting these people? Are these representative males themselves? Are the females representative? Does the birth order effect only express itself in this community and these makes in these parts of the country/world/industry? What is its suggested mechanism of action that can be stated in a falsifiable way? If it was real, where else would you find it, and given our known distribution of makes in the population, how often and strong might you expect those effects to be?