Data Dictionary:  Census 2000 
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Survey: Census 2000
Data Source:  U.S. Census Bureau 
Data set: Summary File 3 (SF3)
Table:  P4. Percent Of The Population In Sample [1] 
Universe: Total population
Table Details
P4.  Percent Of The Population In Sample  
Universe: Total population  

Notes:
Summary File 3 is a sample (a subset of a population) survey enumerating approximately one in six households. Numbers are then adjusted to "estimate" the population based on the sample.
On the other hand, Summary File 1 enumerates 100percent of the population, so "Percent of the population in sample" table in SF3 shows the quality of the SF3 sample compared to the 100% count.