National Panel Survey 2008-2009

In order to monitor progress toward the MKUKUTA goals, it was vital that the NPS have a nationally-representative sample design. As such, in 2008/09 the NPS interviewed 3,280 households spanning all regions and all districts of Tanzania, both mainland and Zanzibar.

The sample size of 3,280 households was calculated to be sufficient to produce national estimates of poverty, agricultural production and other key indicators. It will also be possible in the final analysis to produce disaggregated poverty rates for 4 different strata: Dar es Salaam, other urban areas on mainland Tanzania, rural mainland Tanzania, and Zanzibar. Alternatively, estimates of most key indicators can be produced at the zone level, as used for the Demographic and Health Survey (DHS) reports and other surveys. There are 7 of these zones in total on the mainland: North, Central, Eastern, South, Southern Highlands, West and Lake. As with any survey though, the confidence of the estimates declines as statistics are disaggregated into smaller zones.

Due to the limits of the sample size it is not possible to produce reliable statistics at the regional or district level.

The guiding principle in the choice of sample size, following standard practice for NBS surveys, was to produce estimates with a 95% confidence interval no larger than 5% of the mean for key indicators. In this case, household consumption and maize yields were used as the basis for those calculations.

The NPS was based on a stratified, multi-stage cluster sample design. The principle strata were Mainland versus Zanzibar, and within these, rural versus urban areas, with a special stratum set aside for Dar es Salaam. Within each stratum, clusters were chosen at random, with the probability of selection proportional to their population size. In urban areas a 'cluster' was defined as a census enumeration area (from the 2002 Population and Housing Census), while in rural areas an entire village was taken as a cluster. This primary motivation for using an entire village in rural areas was for consistency with the HBS 2007 sample which did likewise.

Based on the 2002 Population and Housing Census, rural residents comprise roughly 77% of the population, compared with 63% of the NPS sample. The NPS sample gives slighter greater weight to urban areas due to the higher levels of inequality in these areas, and added difficulty in estimating poverty rates and other statistics. Similarly, Zanzibar comprised roughly 3% of the Tanzanian population in the 2002 census, but constitutes nearly 15% of the NPS sample, so as to allow separate Zanzibar-specific estimates to be presented for most indicators.

Finally, although it has been stressed that the 2008/09 round is the first year of the NPS, the sample design for year 1 was deliberately linked to the 2007 HBS to facilitate comparison between the surveys. On mainland Tanzania, 200 of the 350 in the NPS were drawn from the 2007 HBS sample (this included all 140 rural HBS clusters). Within these 200 HBS clusters, a portion of the (8) households sampled for the NPS were taken from the sample of (24) HBS households in the cluster. (The number of HBS households sampled varied from cluster to cluster, in proportion to the share of the population, as measured through a comprehensive household listing, that had remained stationary in the cluster since the time of the HBS. This was done to ensure that the NPS sample remained nationally representative despite possible non-random attrition of HBS households.)

This design created a panel of approximately 1,200 HBS households - interviewed in both the HBS and NPS - within the total sample of 3,280 NPS households.