I only have anecdotal evidence from this specific forum, but I guess my general impression is that men are actually more likely to stay. Maybe I am assuming that based on the number of women in the S/D forum? But there may be more women on the site, or women may be more active posters, or I may notice my own gender and follow their stories more closely on a subconscious and unintentional level. There are a lot of explanations.
Why are the averages important to you?
Even when every other story you read here feels familiar, each situation and each pair of people is unique - there are rarely generalizations or averages that can help us heal or move forward.