Objective: Consultants employed by the NHS in England are allowed to undertake private practice to supplement their NHS income. Until the introduction of a new contract from October 2003, those employed on full-time contracts were allowed to earn private incomes no greater than 10% of their NHS...

The need to use multilevel models when analysing hierarchical data—to take account of the correlation in the data when estimating regression coefficients—is widely recognised in health research.1,2 The advantages afforded by multilevel models—including the ability to partition variation to...

The system GMM estimator for dynamic panel data models combines momentconditions for the model in first differences with moment conditions for the model inlevels. It has been shown to improve on the GMM estimator in the first differencedmodel in terms of bias and root mean squared error....

The system GMM estimator for dynamic panel data models combines moment conditions for the model in first differences with moment conditions for the model in levels. It has been shown to improve on the GMM estimator in the first differenced model in terms of bias and root mean squared error....