NATIONAL BUREAU OF ECONOMIC RESEARCH
NATIONAL BUREAU OF ECONOMIC RESEARCH

NBER Working Papers by John Ham

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Working Papers

June 2010Estimating Heterogeneous Treatment Effects of Medicaid Expansions on Take-up and Crowd-out
with I. Serkan Ozbeklik, Lara Shore-Sheppard: w16112
Economists have devoted considerable resources to estimating local average treatment effects of expansions in Medicaid eligibility for children. In this paper we use random coefficients linear probability models and switching probit models to estimate a more complete range of effects of Medicaid expansion on Medicaid take-up and crowd-out of private insurance. We demonstrate how to estimate, for Medicaid expansions, the average effect among all of those eligible, the average effect for a randomly chosen person, the effect for a marginally eligible child, and the average effect for those affected by a nonmarginal counterfactual policy change. We then estimate the average effect of Medicaid expansions among all eligible children and the average effect for those affected by a nonmarginal cou...
July 2009Seam Bias, Multiple-State, Multiple-Spell Duration Models and the Employment Dynamics of Disadvantaged Women
with Xianghong Li, Lara Shore-Sheppard: w15151
Panel surveys generally suffer from “seam bias”--too few transitions observed within reference periods and too many reported between interviews. Seam bias is likely to affect duration models severely since both the start date and the end date of a spell may be misreported. In this paper we examine the employment dynamics of disadvantaged single mothers in the Survey of Income and Program Participation (SIPP) while correcting for seam bias in reported employment status. We develop parametric misreporting models for use in multi-state, multi-spell duration analysis; the models are identified if misreporting parameters are the same for fresh and left-censored spells of the same type. We extend these models to allow misreporting to depend on individual characteristics and for a certain fract...
November 1991Estimating the Effect of Training on Employment and Unemployment Durations: Evidence From Experimental Data
with Robert J. LaLonde: w3912
Using data from a social experiment, we estimate the impact of training on the duration of employment and unemployment spells for AFDC recipients. Although an experimental design eliminates the need to construct a comparison group for this analysis, simple comparisons between the average durations or the transition rates of treatments' and controls' employment and unemployment spells lead to biased estimates of the effects of training. We present and implement several econometric approaches that demonstrate the importance of and correct for these biases. For the training program studied in the paper, we find that it raised employment rates because employment durations increased. In contrast, training did not lead to shorter unemployment spells.

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