摘要：Population estimates are generally drawn from one point in time to study disease trends over time;
changes in population characteristics over time are usually not assessed and included in the study
design. We evaluated whether population characteristics remained static and assessed the degree
of population shifts over time. The analysis was based on the New York State 1990 and 2000 census
data with adjustments for changes in geographic boundaries. Differences in census tract
information were quantified by calculating the mean, median, standard deviation, and the percent
of change for each population characteristic. Between 1990 and 2000, positive and negative
fluctuations in population size created a U-shaped bimodal pattern of population change which
increased the disparities in demographics and socioeconomic status for many census tracts. While
268 (10%) census tracts contracted by 10%, twice as many census tracts (21%, N = 557) grew at
least 10%. Notably, the non-Hispanic African-American population grew 10% or more in 152 tracts.
Although there were overall reductions in working class and undereducated populations and gains
in incomes, most census tracts experienced growing income inequalities and an increased poverty
rate. These changes were most pronounced in urban census tracts. Differences in population
characteristics in a decade showed growing disparities in demographics and socioeconomic status.
This study elucidates that important population shifts should be taken into account when
conducting longitudinal research.
