MOTIVATION Univariate Cox regression (COX) is often used to select genes possibly linked to survival. With non-proportional hazards (NPH), COX could lead to under- or over-estimation of effects. The effect size measure c=P(T(1)<T(0)), i.e. the probability that a person randomly chosen from group G(1) dies earlier than a person from G(0), is independent of the proportional hazards (PH) assumptio...

The use of the Cox proportional hazards regression model is widespread. A key assumption of the model is that of proportional hazards. Analysts frequently test the validity of this assumption using statistical significance testing. However, the statistical power of such assessments is frequently unknown. We used Monte Carlo simulations to estimate the statistical power of two different methods ...

A major assumption of the Cox proportional hazards model is that the effect of a given covariate does not change over time. If this assumption is violated, the simple Cox model is invalid, and more sophisticated analyses are required. This paper describes eight graphical methods for detecting violations of the proportional hazards assumption and demonstrates each on three published datasets wit...

Background: Clinical prediction rules (CPRs) should be externally validated by independent researchers. Although there are many cardiovascular CPRs, most have not been externally validated. It is not known why some CPRs are externally validated by independent researchers and others are not. Methods: We analyzed cardiovascular risk CPRs included in a systematic review. Independent external valid...

BACKGROUND The aim of this prospective study was to evaluate the value of F-18-fluorodeoxyglucose-positron emission tomography (FDG-PET) for early assessment of chemotherapy response in patients with advanced colorectal cancer. METHODS Dynamic FDG-PET was carried out before and at 2 (n = 50) and 6 months (n = 19) after the start of treatment. Quantitative Patlak analysis [metabolic rate of gl...