Number of PSUs and Cluster Size
Survey costs depend not only on number of households but their distribution among Primary Sampling Units (PSUs).
In general, the more PSUs the better for reliability but the greater the cost (usually travel costs).
We recommend 300 to 400 PSUs or more.
Number of PSUs also depends on cluster size.
Cluster size should be as small as practical for reliability.
Example: 8000 households selected in 400 PSUs of 20 households each is much more reliable sample than 200 PSUs of 40 each, but more expensive.