The history of NSS surveys can be divided into three phases:the formative years (1st to 10th round), the period of growth and consolidation (11th to 27th round) and the period after formation of NSSO (since 28th round). The 28th round of NSS (October 1973-June 1974) marks a significant watershed in the evolution of NSS as it introduced major changes in the design.
The basic design followed is stratified two-stage (for smaller villages / urban blocks) or three-stage (for larger villages/blocks involving hamlet group/sub-block formation). The primary stage unit (PSU) is Village (in rural areas) or Urban Frame Survey Block (in urban areas), but the ultimate stage unit (USU) is invariably household/enterprise for household/enterprise surveys. However most of the NSS surveys being multi-subject integrated ones, detail design varies from survey to survey.