I've read that certain conditions promote females vs. males. If I recall, the source I saw claimed 20/4 during veg produced the greatest likelihood of females. Other factors where mentioned too, like temp and other things. But I never saw the root source of that assessment or any data to back up the claim. I figure different variables could play off one another...such as temps in X range like Y amount of light while temps in A range like B amount of light, and so on making the whole thing rather complicated leading you back to square one--a crap shoot. Who knows? Not I.