China's 2016 universal two-child policy made the second-child decision a live question for millions of one-child mothers, yet realized births have remained far below what intention surveys predict. Liu and Lummaa (2019) showed, in a Xi'an survey of one-child mothers, that this decision unfolds in steps — ideal family size, fertility desire, fertility intention — with different factors, including the husband's and the firstborn child's attitudes, acting at each step; the authors' own follow-up (Zhang, Liu and Lummaa, 2022) found that only about half of positive second-child intentions became a live birth within three years, and that the husband's and firstborn's emotional support raised birth hazards over and above the mother's stated intention. The open problem is whether this multi-step, multi-actor decision structure and its partial intention realization generalize prospectively beyond the Xi'an panel; how husband–wife and parent–offspring disagreement over additional childbearing emerges and shapes realized fertility when family members are measured directly; the relative contributions of cultural transmission versus evolved family conflicts to fertility trends; and whether candidate policy interventions suggested by the framework's own findings causally affect childbearing intentions and behavior. The common objective is a validated account of how multi-member family decision processes convert into China's persistently low second-birth rates.

Background

China relaxed its long-running one-child policy (approximately 1979–2015) to a universal two-child policy in 2016 and a three-child policy in 2021, yet fertility has stayed far below replacement level, making the drivers of second-child decisions a central question for Chinese demography. A classic finding in demography and social psychology — formalized in Ajzen's (1991) theory of planned behavior, which models behavioral intention as the proximate antecedent of action — is that stated intentions predict behavior only imperfectly; in fertility research this intention–behavior gap means intention surveys systematically overpredict births. 'One-child mothers' are women whose only child was born under the one-child policy; for them, the 2016 reform converted a previously forbidden parity transition into an actual decision.

Liu and Lummaa (2019) studied this decision with a framework splitting it into three steps — ideal family size (how many children one considers ideal), fertility desire (whether one personally wants another child), and fertility intention (whether one actually plans to have one) — and emphasized that the family contains multiple decision-makers, notably the husband and the already-born ('firstborn') child. Using the 2015 Xi'an Fertility Survey of 560 one-child mothers, they found that different factors act at different steps: the mother's own attitudes toward two children shaped her ideal family size; the husband's and the firstborn's attitudes were critical for desire; desire in turn played a decisive role in intention; admiration for two-child families — a prerequisite for social learning, i.e., adopting behaviors observed in others — predicted desire; perceived child mortality and the value of children for old-age security predicted ideal size; and physical/economic constraints primarily predicted intention. An evolutionary framing motivates the multi-actor view: parent–offspring conflict (the divergence of genetic interests between parents and offspring over parental investment) and sexual conflict between spouses can push family members in different directions, as documented for China by Liu, Duan and Lummaa (2017) on grandparental pressure over family size. Longitudinal work predating this framework had already shown second-birth intentions to be unstable in Jiangsu province (Bao, Chen and Zheng, 2017).

The authors' own follow-up connected the framework to behavior: Zhang, Liu and Lummaa (2022) conducted an event history analysis (a survival-style analysis of the hazard of giving birth) on 321 one-child mothers followed from 2015 to 2018 in the Xi'an Fertility Survey. Only 50% of positive second-child intentions were realized as a live birth within three years, while 15% of uncertain and 5% of negative intentions also ended in a birth; the husband's and the firstborn child's emotional support raised the hazard of a second birth only partly through the mother's intention, and thus directly contributes to the intention–behavior gap. That study, however, was confined to the Xi'an panel, measured the husband's and the child's attitudes only through the mother's perception, and acknowledged a modest sample size and imprecise counting of pregnancies and their outcomes.

Problem Statement

The overarching objective is a validated account of how second-birth decisions are formed within multi-member families and translated into realized births in China's low-fertility context, sufficient to identify which family-level and policy levers raise the realization of intended births. Building on Liu and Lummaa (2019) and Zhang, Liu and Lummaa (2022), the following are unresolved:

(1) External validity: does the step-specific predictor structure — including the husband's and the firstborn child's attitudes and the family emotional-support effects established in Xi'an — and the partial realization of intentions (roughly half of positive intentions converting to births within three years) hold prospectively in other geographic regions, socioeconomic strata, and policy eras (two-child versus three-child), when baseline stepwise decision states are linked to subsequently realized second births?

(2) Intrafamilial disagreement mechanisms: when attitudes and support are measured directly from husbands and firstborn children themselves rather than only through the mother's perception, when and why do husband–wife and parent–offspring disagreements over having another child emerge, and how do disagreement versus support translate into fertility behavior — thereby explaining intrafamilial sources of low parity?

(3) Macro-level drivers: what are the relative contributions of cultural transmission (for example, diffusion of admiration for two-child families) and evolved family conflicts (sexual conflict between spouses; parent–offspring conflict) to population-level fertility trends?

(4) Intervention: do candidate levers aligned with the framework's findings — family-harmony programs, media campaigns increasing admiration for two-child families, and measures offsetting age-related constraints — causally affect childbearing intentions and realized fertility?

These components jointly serve one objective — the conversion of family decision processes into births — and are therefore stated together as parts of a single open research program.

References

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