Table 1.

Comparison of 2-dimensional spatial distributions of aggregate structures in observed and theoretical populations¹

Population examined6	Number of structures	Number of squares	Average number of structures/ grid square2	Number of grid squares containing structures
				0	1	2	35
97–863 expected4	154	103	1.50 1.50	15 23.1	40 34.5	38 25.8	10 12.9
97–142 expected	115	104	1.11 1.11	19 35.1	57 38.5	26 21.1	2 7.7
916–150 expected	94	106	0.89 0.89	32 43.7	56 38.7	16 17.2	2 5.1
916–444 expected	74	106	0.70 0.70	45 52.7	49 36.8	11 12.9	1 3.0
920–125 expected	106	106	1.00 1.00	27 39.0	54 39.0	23 19.5	2 6.5
920–400 expected	94	106	0.89 0.89	36 43.7	47 38.7	22 17.2	1 5.1

1. The populations shown in Figure 6 were used to obtain the observed values. 2. The grid square area within which structures were counted was 30.25 mm². 3. Two time points (frames) were measured from each sequence: 86 & 142, 150 & 144, 125 & 400. 4. Expected values are Poisson distributions of theoretical populations with the same average number of structures per grid square. 5. Squares containing 4 (1), 5 (2) and 6 (1) are included for population 97–86. 6. Chi-square and p values were obtained by comparison of the observed and theoretical populations divided into 4 classes. Thus there are 3 degrees of freedom for all populations. The values obtained are: 97–86: 10.1, p = .017; 97–142: 21.6, p = .0001; 916–150: 12.8, p = .0048; 916–444: 6.8, p = .086; 920–125: 13.2, p = .0041; 920–400: 7.8, p = .052.