Forecast Households at the County Level: An Application of the ProFamy Extended Cohort-Component Method in Six Counties of Southern California, 2010 to 2040

Abstract

Policymakers and market analysts have long been interested in future trends of households. Among household projection methods, the ProFamy extended cohortcomponent method, as one alternative to the traditional headship-rate method, has recently been extended to the subnational levels. This paper illustrates the application of the ProFamy method at the county level by projecting household types, sizes, and elderly living arrangements for six counties of Southern California from 2010 to 2040, including Imperial, Los Angeles, Orange, Riverside, San Bernardino, and Ventura.Using this specific case, this paper introduces the rationales and procedure of the county-level application of the ProFamy method. The validation test for the ProFamy to project the 2010 population and households using the 2000 census data support the use of the ProFamy at the county level. And the ProFamy method also yields satisfactory results in comparison with the projections of headship-rate methods. The ProFamy forecasts on the six county of Southern California provide detailed information on the county-level trends of households and elderly living arrangement in this region, which are valuable information for the local planning agency but usually beyond the capacity of the traditional methods.

Appendices

Appendix 1

Procedures to Estimate Race-Specific Life Expectancies at Birth for California

As the National Center for Health Statistics (NCHS) only releases life expectancies at birth for California without four race categories, the race-sex-specific life expectancies at birth, e(r), are thus estimated based on the race-specific life expectancies at birth at national level by the following formula (for simplicity, the sex dimension is omitted hereafter):

$$e\left( r \right)\, = \,e\frac{{e_{\text{n}} (r)}}{{e_{\text{n}} }},$$

(1)

where e is life expectancy at birth for all races combined in California, e_n(r) and e_n are race-specific life expectancy at birth and life expectancy at birth for all races combined at national level, released by NCHS. We then adjust e (r) to make sure that the weighted average of e (r) (using proportions of population size of each race group as weight) is equal to e:

$$e^{\prime}\left( r \right)\, = \,e\left( r \right)\frac{e}{{\sum\limits_{r} {\left[ {e(r)p(r)} \right]} }},$$

(2)

where p (r) is the proportion of persons of race r among the total population in the state of California, $\sum\limits_{r} {p(r) = 1.0}$

Procedures to Estimate Race-Specific Mean Age at First Marriage

The national data for median age at first marriage are available from the US Census Bureau (2006), but the state-level data of mean age at first marriage are not available. Using the pooled survey data, we first calculate a sex-specific ratio of mean age at first marriage to median age at first marriage for all races combined at the national level. By applying this ratio to the sex-specific median age at first marriage for all races combined of California published by the US census Bureau (2005), we obtain the all-races-combined sex-specific mean age at first marriage ($\overline{M}$) for California. We then estimate the sex-race-specific mean age at first marriage $\left( {\overline{M} (r)} \right)$ for California using the following procedure:

$$\overline{M} (r)\, = \,\overline{M} *\frac{{\overline{M}_{\text{n}} (r)}}{{\overline{M} {}_{\text{n}}}},$$

where $\overline{M}_{\text{n}}$ and $\overline{M}_{\text{n}} (r)$ are sex-specific mean age at first marriage for all races combined and for race r at national level, both estimated through the pooled survey data. $\overline{M} (r)$ is then adjusted to make sure that the weighted average (using proportions of each race group as weight) is equal to the all-races-combined sex-specific mean age at first marriage in the state of California.

Appendix 2

See Tables 7 and 8

Table 7 Percentage distributions of households types/size and elderly living arrangements in the counties of Imperial, Los Angeles, and Orange, 2010 to 2040

Table 8 Percentage distributions of households types/size and elderly living arrangements in the counties of Riverside, San Bernardino, and Ventura, 2010 to 2040