A reflection on HIV/AIDS research after 25 years

Dr. Robert C. Gallo provides a personal reflection on the 25 year history of AIDS

Calculation of the expected number of failures for a repairable asset system

The expected number of failures is the essential element in cost analysis for a repairable system in engineering asset management. A renewal process is typically used for modelling a repairable system with perfect repairs while a nonhomogeneous Poisson process can be used to model a repairable system with minimal repair. An asset system with imperfect repair will be restored to the state which is somewhere between as bad as old and as good as new. While imperfect repairs are more realistic, it is more challenging to calculate the expected number of failures. In this paper, we propose an imperfect reparable system assuming decreasing restoration levels conditional on the previous repair actions. Compared with a popular imperfect repairable system settings which assumes a constant discount restoration level after the first failure occurrence, our decreasing restoration levels model may better represent the actual repair-restoration patterns for many asset systems. The likelihood function of the newly proposed model is derived and the model parameters can be estimated based on historical failure time data. We adopt a cumulative hazard function based Monte Carlo simulation approach to calculate the expected number of failures for the newly proposed reparable system model. This new simulation algorithm is demonstrated on both simulated and real data and compared to a popular existing model under a Weibull distribution setting. An advantage of our simulation algorithm is that a bootstrap version confidence band on the estimated expected number of failures can easily be constructed. The modelling and simulation results in the paper can be used for the development of a reliability engineering analysis and asset management decision making too

The children's services interview:validity and reliability

BACKGROUND: The Children Service Interview was designed as a brief measure of service use related to mental health problems in Great Britain. METHOD: We validated the Children's Services Interview against medical records from a sample of 87 children, and assessed test-retest reliability from 25 parents completing two interviews. We examined criterion validity by looking at the service use patterns of children attending clinics for different types of disorders. RESULTS: The Children's Services Interview showed high levels of face validity and moderate or better concordance with medical records as far as contacts were recorded in the case notes. Test-retest reliability was moderate or better apart from contacts with the voluntary sector, teachers, and the number and duration of appointments with some professionals. CONCLUSION: The study suggests the Children's Services Interview can extract moderately valid and reliable data on service use. DECLARATION OF INTEREST: Tamsin Ford was supported by a Wellcome Clinical Training Fellowship in Health Services Research while completing this work

Binary geometric process model for the modeling of longitudinal binary data with trend

Geometric process, Longitudinal binary data, Trend data, Threshold model,