本研究假設社經發展是人口數量改變的潛在機轉。在過去50年，台灣經歷了急劇的社經變化和快速的人口變遷。同步方程式因此被引用來整合社經因素探討對年齡別生育率之影響。估計所得的年齡別生育率再用來推計台灣2004-2033 的人口。本研究的低與中推計結果接近行政院經建會同期間的中高推計，而兩者之高推計結果也接近。質言之，假如台灣社經發展呈快速成長總生育率有可能在2033 年反彈到替代水準；假如社經發展呈中度成長，總生育率有可能回升到1.6； 假如社經發展持續下挫，總生育率有可能維持在超低水準。

In this study, we assume that socio-economic development is the underlying mechanism for population changes. In the past 50 years, Taiwan has experienced drastic socio-economic changes and rapid population change. Simultaneous equations are thus used to integrate the effect of Taiwan's socio-economic factors on the projection of its age-specific fertility rate (ASFR). The estimated ASFR is then used to make population projectionsforTaiwanintheperiod2004-2033. The results of our low and medium projections are close to the official (CEPD) medium-high projection for the same time period. The results of the high projection for both studies are rather similar too. Specifically, if Taiwan’s socio-economic development grows at a high variant, its fertility would rebound to replacementlevelby2033. If it follows the medium variant, fertility would rise to 1.6 births per woman. But if Taiwan's future socio-economic development grows sluggishly as in the assumed low variant case, Taiwan's fertility would remain at lowest-low level.