The effect of clustering interval on design effect may be important in selection of alternative sampling designs by evaluating the cost-efficiency in the context of face-to-face interview surveys. There has been little work in investigating this effect in New Zealand. This study attempts to investigate this effect by using data from a two-stage sampling face-to-face interview survey. Seventeen stimulated samples are generated. A simple method, design effect =msb /ms, is developed to estimate design
effects for 81 variables for both the simulated samples and the original sample. These estimated design effects are used to investigate the effect of clustering interval. This study also investigates the effect of cluster size. The results indicate that clustering interval has little influence on design effect but cluster size substantial influence. The evaluation of the cost-efficiency in alternative clustering intervals is discussed. As an improvement in the efficiency of a sample design by an increase in clustering interval can not be justified by the increase in cost, it seems that the sample design with the smallest clustering interval is the best. An alternative method design effect ≈ mr2 is also discussed and tested in estimating design effects. The result
indicates that the applicability of design effect ≈ mr2 is the same as that of design effect = msb /ms.