28 days in70.80 per cent.
30 days in13.74 per cent.
21 days in1.66 per cent.
27 days in1.45 per cent.

As regards the season in which menstruation first appears, Krieger states that in one-half of the women examined by him menstruation had begun in the autumn season, in the month of September, October, or November.

Szukits, as a result of an investigation into the menstrual functions of Austrian women, determined that among 1,013 women menstruation occurred:

Every 28 to 30 days in642 women.
Every 8 to 21 days in169 women.
Every 35 to 56 days in128 women.
And was quite irregular in74 women.

In 500 Jewish women, Hirsch found that menstruation occurred:

23 days after the beginning of the last menstruation in19
24 days after the beginning of the last menstruation in29
25 days after the beginning of the last menstruation in36
26 days after the beginning of the last menstruation in56
27 days after the beginning of the last menstruation in62
28 days after the beginning of the last menstruation in73
275

and in the remaining cases at other intervals than those stated. He is, therefore, of opinion that in the majority of Jewish women the type of menstruation is shorter then twenty-nine days.

According to Brierre de Boismont, among 100 women menstruation recurred:

Every 4 weeks in61 women.
Every 3 weeks in28 women.
Every 2 weeks in1 woman.
And at various irregular periods in10 women.

Tilt found among 100 women that menstruation recurred: