In the empirical literature on assortative matching using linked employer-employee data, unobserved worker quality appears to be "negatively" correlated with unobserved firm quality. We show that this can be caused by standard estimation error. We develop formulae that show that the estimated correlation is biased downwards if there is true positive assortative matching and when any conditioning covariates are uncorrelated with the firm and worker fixed effects. We show that this bias is bigger the fewer movers there are in the data, which is 'limited mobility bias'. This result applies to any two-way (or higher) error components model that is estimated by fixed effects methods. We apply these bias corrections to a large German linked employer-employee data set. We find that, although the biases can be considerable, they are not sufficiently large to remove the negative correlation entirely. Copyright (c) 2008 Royal Statistical Society.

No abstract

Concern about diet and access to healthy foodstuffs is felt worldwide. The introduction of large retailers, with low prices and wide product ranges, to poor access areas has been seen as a solution. We apply quantile regression to data related to one such opening, the Seacroft Intervention Study in the United Kingdom, allowing consideration at different levels of the fruit and vegetable consumption distribution. For residents with easy access to the new store, captured using Ordnance Survey Integrated Transport Network for improved representation of shoppers' journeys, a significant average increase of half a portion per day was found, increasing to 0.7 portions or more for households with no car access. However moving away from the average effects considered in the literature thus far, shopping at the new store is significant only for those at the top end of the distribution and, importantly, not for those whose diets were previously poor. Attitudes to healthy eating, relative cost of fruit and vegetables, and deprivation are shown to be key factors at lower intake levels. Access remains a significant determinant of consumption. Hence we urge caution in accepting the conclusion that new supermarkets can benefit all, and suggest that policy makers should consider more targeted measures to help improve the worst diets.

This article investigates the impact of the introduction of the euro on the interactions across the New York, London, Frankfurt and Paris stock markets. After controlling for possible returns and volatility spillovers, we focus on the correlations of shocks using the framework of Dynamic Conditional Correlations (DCC). Daily pseudo-closing prices (recorded at 16:00 London time) are used to avoid conflating correlation and spillover effects. Statistical break tests confirm that the introduction of the euro significantly affects the cross-market correlations. Although dynamic correlations of shocks between all market pairs increase, the correlation in the post-euro period is highest between Frankfurt and Paris, indicating increased integration of these markets. Other findings include the presence of spillover effects from foreign markets for both returns and volatilities, with asymmetries in volatilities and conditional correlations such that negative shocks have larger effects than positive ones.

No abstract