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In a \(2^{3}\) factorial design with three treatments A, B, C each at two levels, blocks of 4 plots are available. The design is replicated twice and the allocation of treatment combination is :

Replication 1Replication 2
Block IBlock IIBlock IBlock II
1b1a
acbc
bcabacab
abcacabcbc

Hence the two confounded treatment combinations in replication 1 and 2 respectively are :

  • A.AB and ABC
  • B.AB and AC
  • C.BC and ABC
  • D.BC and AC

Answer: D

The confounded effects are BC in replication 1 and AC in replication 2.

A two-factor interaction XY is confounded when one block holds the combinations where X and Y are at the same level and the other block those where they differ.

  • Replication 1, block I = {1, a, bc, abc}: b and c are either both absent or both present, so BC is confounded.
  • Replication 2, block I = {1, b, ac, abc}: a and c are both absent or both present, so AC is confounded.

AB would need a block {1, ab, c, abc}, and ABC a block {1, ab, ac, bc}; neither appears, which rules out options A, B and C.

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