本文主要探討在完全競爭和價格可調整的假設下，總要素生產力(TFP)不確定性外生衝擊對於工作流動的影響機理。首先，基於對美國資料的實證分析，研究發現，不確定性的增加使得人們難以作出經濟決策，造成投資和就業減少；在2008年金融海嘯以後，不確定性衝擊對總體經濟活動的緊縮效應更為顯著，對於工作破壞和工作創造的影響尤為明顯。為進一步檢驗工作流動在因應不確定性衝擊的影響機理，本文在den Haan et al. (2000) 的基礎上構建了一個考慮投資和勞動調整成本的動態均衡模型。在價格與薪資可靈活調整的假定下，當技術不確定性的外生衝擊增加時，家計單位透過擴大勞動供給而提高謹慎性儲蓄，減少消費，同時投資和就業同步增加。其次，在調整成本函數中同時納入投資和雇傭調整成本的二次項及其交互項，可以更好地解釋美國總體經濟的波動性。如果將二次項的勞動調整成本排除會使得模型與美國實證資料相比有較大的偏误，而僅僅不考慮資本調整成本則不會造成這種偏误。再次，工作創造的正向反饋效應相對於工作毀滅而言更大。透過降低內生的工作毀滅，可以放大總要素生產力不確定性對總體經濟的擴張效應。最後，投資技術的不確定性衝擊和總要素生產力不確定性的衝擊方向一致，亦為擴張性的。而消費偏好的不確定性衝擊擴大消費及就業，同時抑制投資和產出。本文亦发现，當交互項調整成本的係數為負且足夠小時，不確定性衝擊會抑制謹慎性儲蓄，減少投資和就業。

Positive spillovers of uncertainty shocks have been a driving force behind job flows dynamics, particularly with lower endogenous job destructions. Empirically, the increased volatility in uncertainty leads to a reduction in investment and employment especially after the Great Recession of 2008. To investigate the mechanism behind the movements of job flows in react to uncertainty shock, we quantify dynamic effects of uncertainty by constructing a dynamic general equilibrium model based on den Haan et al. (2000). In our model, uncertainty shocks are mainly defined as increases in technology volatility shocks. Firms expand investment and hiring following a total factor productivity (TFP) uncertainty shock as prices or wages are flexible.

Incorporating quadratic factor adjustment costs and negative interaction of investment and hiring costs into adjustment cost function better accounts for volatility of macroeconomic aggregates within the United States. Discounting quadratic labor adjustment costs leads to unexpected bias while ignoring capital adjustment costs does not. The effects of investment specific uncertainty shocks are as expansionary as that of TFP uncertainty shocks while preference uncertainty shocks increase consumption and employment while contracting investment, which matches the U.S. evidence closer. If in a model with highly negative slope of the interaction adjustment costs, macroeconomic aggregates contract except for consumption, which is subdued after an initial increase in response to uncertainty shocks.

The job creation margin magnifies the responsiveness of the expansionary effects of TFP uncertainty shocks. The role played by worker's bargaining power is significant.

``````````````1 Introduction 1
2 Evidence 3
3 The Benchmark Model 4
3.1 Labor Market . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2 The Representative Household . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3 The Final Goods Producers . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4 Wage Bargaining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.5 The Government . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.6 Search Equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4 Calibration 10
5 Simulation Method 11
6 Numerical Results 12
7 Sensitivity Analysis 14
8 Conclusions 15
A Tables 17
B Figures 19
C Mathematical Appendix 34
C.1 The Representative Household . . . . . . . . . . . . . . . . . . . . . . . . 34
C.2 Final Goods Producers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
C.3 Wage Bargaining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
C.4 Stationary Equilibrium Conditions . . . . . . . . . . . . . . . . . . . . . 39
C.5 Equilibrium Conditions in Steady State . . . . . . . . . . . . . . . . . . . 40

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