Table 1. Sampling designs for each survey.

Category	1991	1997	2001	2006	2010	2015	2023
Survey area	Nationwide (Excluding Jeju)						Nationwide (Including Jeju)
Survey target	Adults, male and female, aged 18 and over				Adults, male and female, aged 19 and over		Citizens aged 15 and over
Sample size^a	1,500 people	1,500 people	1,514 people	1,018 people	1,004 people	1,000^b people	1,000 people
Sample extraction	Multi-stage stratified random sampling				Multi-stage stratified followed by cluster sampling	Stratified cluster proportional systematic sampling
Sampling error (95% confidence Level)	± 2.5%p			± 3.1%p

Valid sample size only
Weighted sample size