Table 2.--Comparability indexes for groupings of black ducks and percentage change between years 
Area-year 
comparisons 
Pairs 
Characteristics compared 
Flocks of 5 
Singles Threes or more 
Comparability 
index!/ 
Percent change 
ducks per segment 
Southern Zone 
1955-63 
2 
2 
1 
2 
7 
-15 
1955-64 
2 
1 
1 
2 
6 
+16 
1956-63 
2 
2 
2 
2 
8 
- 8 
1956-64 
1 
1 
2 
2 
6 
+26 
Central Zone 
1955-63 
2 
2 
1 
1 
6 
-13 
1955-64 
2 
1 
0 
1 
4 
-28 
1956-63 
1 
2 
2 
2 
7 
-21 
1956-64 
1 
1 
1 
2 
5 
-34 
Northern Zone 
1955-63 
1 
1 
2 
1 
5 
+72 
1955-64 
2 
2 
1 
1 
6 
-10 
1956-63 
1 
0 
1 
1 
3 
+91 
1956-64 
1 
1 
0 
1 
3 
0 
1955-56 
Southern Zone 
2 
2 
1 
2 
7 
- 8 
Central Zone 
1 
2 
1 
1 
5 
+ 9 
Northern Zone 
2 
1 
1 
2 
6 
-10 
1963-64 
Southern Zone 
2 
1 
2 
2 
7 
+38 
Central Zone 
2 
1 
1 
2 
6 
-17 
Northern Zone 
1 
1 
1 
0 
3 
-48 
y Index of 8 indicates highest degree of comparability with regard to grouping characteristics. 
