Table 1.

The number of participants (male and female) who produced usable data at each month.

Age (months)	No. of boys	No. of girls	Total
4	35	40	75
5	40	40	80
6	44	40	84
7	41	40	81
8	41	38	79
9	39	33	72
10	32	26	58
11	30	25	55
12	25	23	48
13	26	18	44
14	18	14	32
15	16	13	29
16	18	11	29
17	15	9	24
18	13	8	21
19	12	7	19
20	12	6	18
21	11	6	17
22	8	6	14
23	3	5	8
24	5	5	10