The Determinants of Household Size Decline in Iran Over the Last Four Decades

Despite a significant rise in demographic knowledge and related studies in Iran over the recent decades, lower attention has been paid to household demography, particularly, changes in the average household size in Iran. Most conducted studies are mainly cross-sectional, small-scale and/or descriptive. The present study investigated the changes in the average household size, and its determinants in Iran over the period 1984-2018 using a longitudinal approach (quasi-panel) and based on the Household Income and Expenditure Survey (HIES) data. The results revealed that the average household size has decreased about an average of 2 people (from 5.4 persons per household in 1980s to 3.4 in 2010s). Moreover, the results of space-state time-series models showed that the effect of variables of fertility, marriage and urbanization on household size has been reduced, while the negative effects of divorce, life expectancy, inflation rate and housing costs have been risen over this period. Based on hierarchical age-period-cohort models, the presence of people in different cohorts has also affected their household size. This result shows that in addition to period analysis, cohort approach should be taken into account for a better understanding of changes in the demographic phenomena across time because people in various cohorts usually have distinctive experiences which may lead to different behaviors.