2015-2040年日本家庭人口预测

Introduction “Household Projections for Japan (Outline of Results and Methods)” projected the number of householdsnationwide and was released in 2018. The initial population used as the benchmark of the projections was obtainedby adjusting the results of the 2015 Census. I. Framework of Projections 1. Period of Projections The period for the present projections is the twenty-five years from October 1, 2015 to October 1, 2040. 2. Method and Results of Projections The essential part of the household projections was carried out by the household transition method. This methodprojects distributions by combination of future marital states and household positions, by setting transitionprobabilities of membersprivate households, and applies them to the population by sex and five-year age group of“Population Projections for Japan (Published in 2017)”2)(medium fertility/medium mortality variant) in order toproject the population by sex, five-year age group, and combination of marital state and household positions.Households are identified with markers such as “one-person households,” “couple-only households,” “couple-and-child(ren) households,” “one-parent-and-child(ren) households,” and “other households.” Markers refer to membersregarded as key persons in terms of household formation/dissolution in projection models and usually match with thehousehold heads of the Census. For exceptional cases such as a wife or a child becoming the head of “couple-and-child(ren) households,” we set certain rules such as the marker of “couple-and-child(ren) households” always beingthe husband and the marker of “one-parent-and-child(ren) households” always being the parent. We applied thecorrespondence between head/non-head and marker/non-marker in 2015 to the projected population by sex, by five-year age group, and by marital state and household positions (marker/ non-marker) to obtain the number of heads bysex, five-year age group, marital state, and family type. The detailed results of the projections are shown in Result Table 1 (Number of Private Households by Family Type,Mean Household Members, Mean Size of Households) and Result Table 2 (Number and Percentages of PrivateHouseholds by Head's Sex and Five-year Age Group, by Family Type). 3. Initial Population We obtained the initial population used as the benchmark of the projections based on the 2015 Census, byconverting positions of members within private households from heads/non-heads by family type to markers/non-markers by family type. 4. Variants of Projections The present projections handle only one case. Additionally, for reference, we also calculated the number ofhouseholds under the assumption that the distributions by sex, five-year age group, and combination of marital stateand household positions remain constant from 2015 and onward. The purpose of the projections is to obtain a future number of private households by family type. This report dealswith five different family types: “one-person households,” “couple-only households,” “couple-and-child(ren)households,” “one-parent-and-child(ren) households,” and “other households.”3)(Table 1) II. Overview of Projection Results 1. Number of Private Household Members and Total Number of Private Households (Figure 1) The total population of Japan has started declining from around 2010. According to the present householdprojections, the development of the number of private household members shows generally the same trends as thetotal population. As seen in Result Table 1, the number of private household members decreases year by year from124.3 million people in 2015 to 157.0 million in 2040, which is a reduction of 18.6 million people. On the other hand, the total number of private households, as shown in Figure 1, continues to grow from 53.33million in 2015 to peak out at 54.19 million households in 2023. Afterward, however, the number starts to decreaseand the total number of private households in 2040 is 50.76 million, which is smaller by 2.57 million than in 2015. 2. Mean Size of Households (Figure 2) The fact that the number of households continues to increase even under the population decline implies that thehousehold size keeps on shrinking. The mean size of private households will continue to decrease, from 2.33 membersin2015to2.08in 2040. 3. Number and Percentage of Private Households by Family Type (Table 2, Figure 3) As shown in Table 2 and Figure 3, the number of “couple-and-child(ren) households” and “other private households”continues to decrease from 2015. The number of “one-person households”, “couple-only households” and “one-parent-and-child(ren) households” will continue to grow for several decades but eventually starts declining in the2030s. The number of “one-person households” keeps on increasing from 18.42 million in 2015 and peaks out in 2032.The number in 2040 is projected to be19.94million, which is 1.53 million larger than2015. Its percentage out of thetotal number of private h