Performance of methods to conduct mediation analysis with time-to-event outcomes

Previous studies have discouraged the use of the Cox proportional hazards (PH) model for traditional mediation analysis as it might provide biased results. Accelerated failure time (AFT) models have been proposed as an alternative for Cox PH models. In addition, the use of the potential outcomes framework has been proposed for mediation models with time-to-event outcomes. The aim of this paper is to investigate the performance of traditional mediation analysis and potential outcomes mediation analysis based on both the Cox PH and the AFT model. This is done by means of a Monte Carlo simulation study and the illustration of the methods using an empirical data set. Both the product-of-coefficients method of the traditional mediation analysis and the potential outcomes framework yield unbiased estimates with respect to their own underlying indirect effect value for simple mediation models with a time-to-event outcome and estimated based on Cox PH or AFT.     

Measuring the systemic risk transfer from the United States to the South African financial sector

The sub-prime crisis in 2008 illustrated how systemic risk in the financial sector of one country could spread to the financial sectors in other countries, and subsequently result in a global financial crisis. This direct transfer of systemic risk was made possible by phenomena such as contagion and common shocks. The way in which these elements of interconnectedness can magnify seemingly small levels of systemic risk, and subsequently transfer between financial sectors illustrate the necessity for a more in-depth analysis. This measurement is done using three approaches. A dynamic conditional correlation (DCC) model is used to investigate contagion. To analyse the volatility spillover effect from the US to SA, an exponential generalized autoregressive conditional heteroskedastic (EGARCH) model is employed. Finally, a new contribution is made where a marginal expected shortfall (MES) model is used to set the FTSE/JSE All-Share Index (ALSI) as a hypothetical bank in the financial sector of the S&P 500. All approaches show weak evidence for a direct systemic risk transfer and therefore indicate that any systemic risk transfer is more likely to take an indirect form through changes in capital flows or interest rates.     

National and provincial PPPs: Issues of supervision and accountability

This article focuses on the key requirements for an enabling framework for the implementation of public‐private partnerships (PPPs) in South Africa. It contends that such an enabling framework should facilitate coherent government policies and legislation, secure procurement reform, enhance capacity, foster stringent ‐ albeit not constraining ‐financial regulation and put in place supportive institutional arrangements. Arguing that PPPs revolve around risk sharing between the public and private sector, value for money and affordability, key features of the South African policy environment as it affects PPPs are discussed. Amid considerable progress, policies across sectors could still be better aligned, legislative inconsistencies straightened out, procurement procedures and approaches updated to focus more sharply on value for money (rather than lowest price) and financial uncertainties countered. It is also noted that PPPs currently occur in an institutional vacuum in the public sector. It is therefore proposed that a dedicated institutional capacity be created to support PPPs more effectively.