AN APPRAISAL OF HOUSEHOLD INCOME AND EXPENDITURE SURVEY DESIGN

The Central Statistical Office (CSO), Botswana and Statistics South Africa conduct large scale nationwide surveys on a regular basis. Both the organizations very often use the same survey design recommended by the UNDP. The survey design involves selection of first stage units (fsu's) with inclusion probability proportional to size (IPPS) sampling design introduced by Goodman and Kish (1950) and the second stage units (ssu's) by systematic sampling scheme. CSO, Botswana employed the same sampling design for "Household Income and Expenditure Survey 2002/03 (HIES, 2002/03)" and " Botswana Aids Impact Survey II, 2004 (BAIS II, 2004)". Chaudhuri and Arnab (1982) proved that for the sampling design recommended by UNDP, the variance of the population total or mean cannot be estimated unbiasedly. Unbiased variance estimation is required for estimating precision of the survey estimates, confidence interval, optimum sample size and testing of hypothesis amongst others. The optimum sample size is the key factor of determination of cost of a survey and precisions of estimates. CSO used design factor 2.0 for determination of sample size which was calculated from the " Household Income and Expenditure Survey, 1993/94 (HIES 1993/94). In our present investigation we have proposed a few alternative sampling designs to overcome the problems of variance estimation. The performances of the estimators are tested with the live data collected by CSO for HIES survey with six indicators. The investigation reveals that the design effect assumed by CSO is very high. It actually varies between 0.85 to 1.31 for all the six indictors of the existing (CSO) and proposed alternative designs. Neither the CSO design nor the proposed alternatives is found suitable for all the indicators. Hence for the consideration of variance estimation one should employ Rao-Hartley-Cochran (RHC) or Simple random sampling without replacement (SRSWOR) for the selection of first stage units and SRSWOR for the selection of second stage units.