Age when girls menstruate

Use this diagram to introduce the idea of predicting the proportion menstruating from age.

Click Stacked. The proportion menstruating increases steadily with age.

Bar charts have been used to convey the ideas. However age is a numerical variable that has been grouped into classes whose widths are unequal, so histograms (and stacked histograms) would describe the data better. In particular, bar charts of the frequencies do not describe the distribution of ages well.

A study was conducted in Warsaw to determine the proportions of girls who had started menstruating at different ages. A total of 3898 girls of various ages between 8 and 19 were asked whether they had started menstruating.

Menstruation
Age class (to nearest month)   Menstruating     Total girls  
8 yr 6 mths - 9 yr 11 mths
9 yr 12 mths - 10 yr 5 mths
10 yr 6 mths - 10 yr 8 mths
10 yr 9 mths - 10 yr 11 mths
10 yr 12 mths - 11 yr 2 mths
11 yr 3 mths - 11 yr 5 mths
11 yr 6 mths - 11 yr 8 mths
11 yr 9 mths - 11 yr 11 mths
11 yr 12 mths - 12 yr 2 mths
12 yr 3 mths - 12 yr 5 mths
12 yr 6 mths - 12 yr 8 mths
12 yr 9 mths - 12 yr 11 mths
12 yr 12 mths - 13 yr 2 mths
13 yr 3 mths - 13 yr 5 mths
13 yr 6 mths - 13 yr 8 mths
13 yr 9 mths - 13 yr 11 mths
13 yr 12 mths - 14 yr 2 mths
14 yr 3 mths - 14 yr 5 mths
14 yr 6 mths - 14 yr 8 mths
14 yr 9 mths - 14 yr 11 mths
14 yr 12 mths - 15 yr 2 mths
15 yr 3 mths - 15 yr 5 mths
15 yr 6 mths - 15 yr 8 mths
15 yr 9 mths - 15 yr 11 mths
15 yr 12 mths - 19 yr 3 mths
0
0
0
2
2
5
10
17
16
29
39
51
47
67
81
88
79
90
113
95
117
107
92
112
1049
376
200
93
120
90
68
105
111
100
93
100
108
99
106
105
117
98
97
120
102
122
111
94
114
1049