Table 1.

Breakdown of subject participation for each age level. Age at which subject was tested, with ‘x’ indicating when tested.

Subject no.	12 Month	15 Month	18 Month	21 Month	24 Month
1					x
2		x
3		x	x
4			x	x	x
5				x
6	x	x	x	x	x
7	x	x		x	x
8	x	x			x
9	x	x		x	x
10	x		x		x
11			x	x	x
12				x	x
13		x		x	x
14		x		x
15	x	x		x
16				x	x
17			x	x	x
18	x	x
19	x	x	x	x	x
20				x
21			x	x	x
22
23			x	x	x
24	x	x	x	x	x
25	x		x	x	x
26	x	x
27					x
28	x		x	x	x
29		x	x	x	x
30	x	x
31	x
32	x	x
33	x
34	x	x
35	x	x
36	x
37	x		x	x	x
38		x
39			x	x	x
40				x	x
41			x		x
42			x
43			x		x
44			x		x
Total	20	19	19	23	26