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Rate of don’t know responding for each survey year and estimated number of don’t know responses in the US adult population
| Prevalence of don’t know response by year
| ||
|---|---|---|
| Survey year | % Don’t know responses | Estimated US adult don’t know responders |
| 1993 | 2.4 | 5,049,888 |
| 1994 | 1.7 | 3,606,074 |
| 1995 | 1.6 | 3,420,480 |
| 1996 | 1.3 | 2,800,356 |
| 1997 | 1.3 | 2,824,640 |
| 1998 | 1.1 | 2,412,674 |
| 1999 | 1.2 | 2,657,208 |
| 2000 | 1.1 | 2,469,720 |
