Sex and the Town

My hometown had a firework festival this evening. I watched the firework from the outside stairway of the building where I was tutoring a high-school senior. While I was on my way to and back from the workplace, I saw a lot of young couples watching the firework in the crowded street. Naturally, I wondered whether they were going to have sex afterwards. This is because according to a certain statistics, the number of sexual intercourses that the average Japanese couple has in one year is by far the lowest in the world. The less frequent sex, the fewer children...?