There are a number of studies about it. The first was done Princess Marie Boneparte, a distant relative of Napoleon. The next study was a study of studies, and it confirmed these results. Recently, a brand new study was started and they looked for participants until a few months ago. I have not checked how that study is progressing.
What was found was called the 'rule of thumb'. If the tip of the clitoris is closer than 2.5 cm from the vaginal entrance (the length of a thumb, so called 'the rule of thumb') you are almost guaranteed an orgasm from intercourse every time. If it is around 2.5 cm, you will sometimes get an orgasm. If it is further away than 2.5 cm, you have to provide extra stimulation like fingers, a toy or a changed sex position. The breakdown is that about 20% of women are under 2.5 cm, about another 15% around 2.5 cm and 65% over 2.5 cm.
This breaks down almost exactly to the statistics of women and their ability to orgasm from intercourse alone. About 20% of women can just orgasm without any effort. A further 10% will often orgasm without any effort. A further 20% of women found techniques and positions to make them orgasm during intercourse. The other 50% of women thinks it is normal not to orgasm, or are clueless about orgasms during intercourse. Of that 50%, about 10% are anorgasmic (10% of the total, not 10% of the 50%.. So 10% of all women never had an orgasm. Not from sex, oral, fingers or masturbation.after treatment, about 0.5% of all women can and will never reach an orgasm, no matter what.
So in summary, out of every 10 women engaging in intercourse:
2 will always orgasm without any effort
1 will orgasm frequently without any effort
2 willl figure out how it works, and get an orgasm regularly
5 will be frustrated or clueless about orgasms during intercourse
1 in every 200 women will never ever get an orgasm, even with help and treatment, masturbation or sex.
A recent development is the fact that the so-called 'g spot' is now thought to be the deep structures of the clitoral complex being stimulated through the vaginal wall. The little pencil eraser sized glans (head) of the clitoris that you see and feel is quite literally just the tip of the iceberg. It goes deep inside your body. Two bulbs run under your lips towards the anus, and two thin legs runs deep inside your body along the pelvic bone. The internal structures are around 15 cm (or slightly longer).