Tied Wage-Hours Offers and the Endogeneity of Wages

In the standard model of labor supply, each worker is a price taker,where the relevant price is an hourly wage rate which is fixed in the short run, and which does not depend upon the number of hours supplied. With this basic assumption, the wage can be regarded as exogenous for the purpose of estimating a labor supply function. This paper proposes and implements a pair of tests for the exogeneity of wages in a longitudinal labor supply model, and for the particular failure of exogeneity associated with jobs that offer wage-hour packages.The first test is very simple -- it amounts to a test of whether hours Granger -- cause wages at the individual level. The second test involves a simultaneous estimation of labor supply and wage offer equations. Both tests indicate that the offered wage is related to hours worked, though the offer locus is, for this sample, very flat. The principal conclusion is that labor supply equations cannot properly be estimated in isolation from the process generating wages, even when long time series are available on a sample of individuals.

Saving for Retirement: Household Bargaining and Household Net Worth

Traditional economic models treat the household as a single individual, and do not allow for separate preferences of and possible conflicts of interest between husbands and wives. Since wives are typically younger than their husbands and life expectancy for women exceeds that for men, wives may prefer to save more for retirement than do their husbands. This suggests that households in which wives have greater relative bargaining power may accumulate greater net worth as they approach retirement. Most empirical models of net worth in the literature do not include characteristics of both spouses. We present a more complete unitary model of household net worth and find, among couples in the first wave of the Health and Retirement Survey, that the characteristics of both husband and wife are determinants of net worth. We explore the importance of bargaining in marriages of older couples by examining the empirical relationship between their net worth and factors such as relative control over current income sources, relative age, and relative education. We find some evidence that low relative education of wives is associated with low net worth.

Multistep integration formulas for the numerical integration of the satellite problem

The use of two Class 2/fixed mesh/fixed order/multistep integration packages of the PECE type for the numerical integration of the second order, nonlinear, ordinary differential equation of the satellite orbit problem. These two methods are referred to as the general and the second sum formulations. The derivation of the basic equations which characterize each formulation and the role of the basic equations in the PECE algorithm are discussed. Possible starting procedures are examined which may be used to supply the initial set of values required by the fixed mesh/multistep integrators. The results of the general and second sum integrators are compared to the results of various fixed step and variable step integrators

Hours Restrictions and Labor Supply

This study presents a model of labor supply in which individuals may face constraints on their choice of work hours, and analyzes the sensitivity of parameter estimates and policy conclusions to the usual assumption of unrestricted choice. We set up the labor supply decision asa discrete choice problem, where each worker faces a finite number of employment opportunities, each offering fixed hours of work.The distribution from which these are drawn, as well as the number of draws, is estimated along with the behavioral parameters of individual labor supply.The standard model with unconstrained hours appears as a special case where the number of draws approaches infinity. We estimate the mean absolute difference between desired and actual work hours to be about ten hours perweek. The results strongly support the notion that hours choices are constrained, and suggest that models which ignore restrictions on hours worked may yield biased estimates of the wage elasticity of desired hours. Further, we suggest that analysis of policies such as income transfers and the flat rate tax which do not consider their effects on the distribution of hours offered may be very misleading.

Saving for Retirement: Household Bargaining and Household Net Worth

Traditional economic models of savings treat the household as a single individual, and do not allow for the separate preferences of and possible conflicts of interest between husbands and wives. Since wives are typically younger than their husbands and life expectancy for women exceeds that for men, wives may prefer to save more for retirement than do their husbands. This suggests that households in which wives have greater relative bargaining power may accumulate greater net worth as they approach retirement. We explore the importance of bargaining in marriages of older couples by examining the empirical relationship between the net worth of couples in the first wave of the Health and Retirement Survey and factors that may affect the relative bargaining power of husbands and wives, such as control over income sources, relative age, and relative education. We find that measures of long-term relative bargaining power of wives have a positive effect on the household's wealth, even when controlling for other factors. In general, the realized effects of reforms intended to increase private saving for retirement may depend on how these reforms affect household bargaining relationships, as well as how they affect individual incentives to save.

Lessons from dynamic cadaver and invasive bone pin studies: do we know how the foot really moves during gait?

Background: This paper provides a summary of a Keynote lecture delivered at the 2009 Australasian Podiatry Conference. The aim of the paper is to review recent research that has adopted dynamic cadaver and invasive kinematics research approaches to better understand foot and ankle kinematics during gait. It is not intended to systematically cover all literature related to foot and ankle kinematics (such as research using surface mounted markers). Since the paper is based on a keynote presentation its focuses on the authors own experiences and work in the main, drawing on the work of others where appropriate Methods: Two approaches to the problem of accessing and measuring the kinematics of individual anatomical structures in the foot have been taken, (i) static and dynamic cadaver models, and (ii) invasive in-vivo research. Cadaver models offer the advantage that there is complete access to all the tissues of the foot, but the cadaver must be manipulated and loaded in a manner which replicates how the foot would have performed when in-vivo. The key value of invasive in-vivo foot kinematics research is the validity of the description of foot kinematics, but the key difficulty is how generalisable this data is to the wider population. Results: Through these techniques a great deal has been learnt. We better understand the valuable contribution mid and forefoot joints make to foot biomechanics, and how the ankle and subtalar joints can have almost comparable roles. Variation between people in foot kinematics is high and normal. This includes variation in how specific joints move and how combinations of joints move. The foot continues to demonstrate its flexibility in enabling us to get from A to B via a large number of different kinematic solutions. Conclusion: Rather than continue to apply a poorly founded model of foot type whose basis is to make all feet meet criteria for the mechanical 'ideal' or 'normal' foot, we should embrace variation between feet and identify it as an opportunity to develop patient-specific clinical models of foot function