Adjusted Populations for the Counties/Parishes Affected by Hurricanes Katrina and Rita
Two sets of population estimates are available for 2005: the standard set based on July 1 populations and a set that has been adjusted for the population shifts due to hurricanes Katrina (August 29) and Rita (September 24). For 62 counties and parishes in Alabama, Mississippi, Louisiana, and Texas, the Census Bureau has provided total population estimates for January 1, 2006 (see Special Processing Procedures for the Areas Affected by Hurricanes Katrina and Rita (PDF)) and estimates by age, sex, and race category for July 1 2006 (see Special Population Estimates for Impacted Counties in the Gulf Coast Area). These data sets were used to develop time-weighted average populations for the 62 counties/parishes in 2005. These estimates are lower than the July 1, 2005 values for counties/parishes that had direct hurricane impact and higher for counties/parishes that were destinations for the people displaced by the hurricanes. The following steps were used:
- For each to the 62 affected counties and parishes, a daily population estimate was created. For the days prior to the hurricane landfall (August 29 for Katrina and September 24 for Rita), a linear model was used based on the July 1, 2004 and July 1, 2005 population estimates.
- For the days after the hurricane, we developed an estimate of the January 1, 2006 population by age, sex, and race category. This estimate was generated by applying a county/parish-wide adjustment based on the January 1, 2006 population estimates to the detailed July 1, 2006 population estimates by age, sex, and race category.
- For the overall 2005 population, we summed the daily estimates and divided by the number of days.
- For population denominators with cancer data, it is usually assumed that the address at diagnosis is the individual’s permanent address. By using the January 1, 2006 population estimates for all of the post-hurricane period, we assume that the current address was used for people who could not return home by January 1, 2006.
- Since these adjustments were made for just 62 counties, the resulting total US population is lower than the July 1 total US population. The difference represents people displaced by the hurricanes who went to other parts of the US. A separate dummy state has been introduced that represents these people. It is labeled “Hurricane Katrina/Rita Evacuees - Populations Only - 2005” and is included by default in rate calculations over the total US.