![]() As a result, any comparison that includes data from before 1990 only includes these three race categories. If the earliest year selected in the tool is from before 1990, the data only includes three race categories: 'white', 'Black', and 'other'. To allow for comparisons over time, the race categories change depending on the earliest year selected in the comparison tool. This occurs because the Census Bureau has changed the race and ethnicity categories it makes available. Users will notice that the race categories change depending on the years selected in this interactive tool. But how the Census Bureau reported and grouped those populations changed over time. However, it is important to note that this data is only as good as the census data on which it is based.The Census Bureau’s Population and Housing Estimates Program (PEP) data by county includes details like counts by age, race, or ethnicity and goes back for decades. Using high-quality, recent census data, the top-down approach provides detailed and valuable representations of the spatial distribution of human populations. ![]() Our statistical modelling techniques are based on the assessment of the relationship between geospatial covariates and population density, while the area-based method distributes the total population evenly either within the corresponding administrative unit or across its building footprints when available. Some national statistical agencies can publish very detailed data whilst others are very generalised (the totals are presented in just a few large administrative units).Ĭensus data as administrative unit totals, particularly when very generalised, can be disaggregated to grid cell level, for example at approximately 100x100m, through statistical modelling techniques or area-based calculations developed by GRID3 partner WorldPop. The size of these units and administrative unit level at which the census data are shared varies between countries. This bottom-up approach does not, however, replace the need for a full census, which usually includes a more precise collection of demographics and socioeconomics, as well as a housing census.Ĭensus data are typically released as administrative unit totals. ![]() Modelling can also fill in data gaps for inaccessible areas. Population modelling can provide more regularly updated population estimates, complementing a decadal population census. In addition, grid cells facilitate the integration of various datasets into the model, providing a consistent framework to work with, and eliminating the impact of inaccuracies in boundary data that can affect the statistical model. ![]() They can be aggregated over various levels of administrative units, but also over areal units that don’t follow administrative boundaries, such as a hospital catchment area. Gridded population estimates at 100x100m resolution are particularly useful as they provide decision-makers and data users with the flexibility to aggregate population estimates into different units in existing enumeration areas or a custom size space. GRID3 uses a Bayesian approach, which allows us to both predict gridded population estimates, and provide the uncertainty surrounding that prediction to help make better-informed decisions.
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