Russel-Research-Method-in-Anthropology

310 Chapter 11
times, and each pair appears n – 2 times. For four items, there are n(n –1)/2
6 pairs; each pair appears twice in four triads, and each item on the list
appears three times.
It is all this redundancy that reduces the number of triads needed in a triads
test. In a complete set of 84 triads for nine items, each pair of items appears
n 2, or seven times. If you have each pair appear just once (called a lambda
1 design), instead of seven times, then, instead of 84 triads, only 12 are
needed. If you have each pair appear twice (a lambda 2 design), then 24 triads
are needed. For analysis, a lambda 2 design is much better than a lambda 1.
Table 11.1 shows the lambda 2 design for 9 items and 10 items.
TABLE 11.1
Balanced Incomplete Block Designs for Triad Tests Involving 9 and 10 Items
For 9 items, 24 triads are
needed, as follows:
For 10 items, 30 triads are
needed, as follows:
Items
Items
1, 5, 9 1, 2, 3 1, 2, 3 6, 8, 9
2, 3, 8 4, 5, 6 2, 5, 8 7, 10, 3
4, 6, 7 7, 8, 9 3, 7, 4 8, 1, 10
2, 6, 9 1, 4, 7 4, 1, 6 9, 5, 2
1, 3, 4 2, 5, 9 5, 8, 7 10, 6, 7
5, 7, 8 3, 6, 8 6, 4, 9 1, 3, 5
3, 7, 9 1, 6, 9 7, 9, 1 2, 7, 6
2, 4, 5 2, 4, 8 8, 10, 2 3, 8, 9
1, 6, 8 3, 5, 7 9, 3, 10 4, 2, 10
4, 8, 9 1, 5, 8 10, 6, 5 5, 6, 3
3, 5, 6 2, 6, 8 1, 2, 4 6, 1, 8
1, 2, 7 3, 4, 9 2, 3, 6 7, 9, 2
2, 4, 8 8, 4, 7
4, 9, 5 9, 10, 1
5, 7, 1 10, 5, 4
SOURCE: Reprinted from Social Science Research, Vol. 5, M. L. Burton and S. B. Nerlove, ‘‘Balanced Design
for Triad Tests,’’ p. 5, 1976, with permission from Elsevier.
For 10 items, a lambda 2 design requires 30 triads; for 13 items, it requires
52 triads; for 15 items, 70 triads; for 19 items, 114 triads; and for 25 items,
200 triads. Unfortunately, there is no easy formula for choosing which triads
in a large set to select for a BIB. Fortunately, Burton and Nerlove (1976)
worked out various lambda BIB designs for up to 25 items and Borgatti has
incorporated BIB designs into Anthropac (1992a, 1992b). You simply tell
Anthropac the list of items you have, select a design, and tell it the number of
informants you want to interview. Anthropac then prints out a randomized