Recent theoretical work has shown the importance of measuring microeconomic uncertainty for models of both general and partial equilibrium under imperfect insurance. In this paper the assumption of i.i.d. income innovations used in previous empirical studies is removed and the focus of the analysis is placed on models for the conditional variance of income shocks, which is related to the measure of risk emphasized by the theory. We first discriminate amongst various models of earnings determination that separate income shocks into idiosyncratic transitory and permanent components. We allow for education- and time-specific differences in the stochastic process for earnings and for measurement error. The conditional variance of the income shocks is modelled as a parsimonious ARCH process with both observable and unobserved heterogeneity. The empirical analysis is conducted on data drawn from the 1967-1992 Panel Study of Income Dynamics. We find strong evidence of sizeable ARCH effects as well as evidence of unobserved heterogeneity in the variances. Copyright Econometric Society 2004.

In this paper we investigate the sensitivity of investmentto the availabilityof internal funds usingthe hierarchy of finance approach to corporate finance. Wecharacterizethe empirical implications of this approach for dynamic investmentmodels and test these implications using firm-level data. The model we estimate is based on the Euler equation for optimal capital accumulation in the presence of convex adjustment costs. The theoretical model explicitly allows for debt finance and financial assets.The empiricalinvestigation usesU.K. company panel data to estimatedynamic investment models using GMM and tests the derived implications.

In October 1999, the working families' tax credit (WFTC) replaced family credit as the main package of in-work support for families with children. Among a range of stated aims, the WFTC is intended to '… improve work incentives, encouraging people without work to move into employment'. In this paper, we consider the impact of WFTC on hours and participation. To simulate labour supply responses, we use a discrete behavioural model of household labour supply with controls for fixed and childcare costs, and unobserved heterogeneity. In simulation, we experiment with a number of scenarios regarding the take-up of the credit, entry wage level and hourly childcare price. We find participation rates among single mothers to increase by around 2.2 percentage points for the base-case scenario, while for married women participation rates are modelled to fall. Our simulation results indicate a small increase in overall participation of around 30,000 individuals.JEL classification: C25, H31, J22.