(Received June 11, 1990; revised June 7, 1991)
Abstract. In this paper the problem of finding the design efficiency is considered when a single observation is unavailable in a connected binary block design. The explicit expression of efficiency is found for the resulting design when the original design is a balanced incomplete block design or a group divisible, singular or semiregular or regular with lambda1 = 0, design. The efficiency does not depend on the position of the unavailable observation. For a regular group divisible design with lambda1 > 0, the efficiency depends on the position of the unavailable observation. The bounds, both lower and upper, on the efficiency are given in this situation. The efficiencies of designs resulting from a balanced incomplete block design and a group divisible design are in fact high when a single observation is unavailable.
Key words and phrases: Balanced incomplete block design, connectedness, efficiency, group divisible design, robustness.
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